The Castlekeep Ruins (aka Old Castle Ruins and Castle Keep Ruins) is the old castlekeep of Daventry predating Edward's castle, but may be more recent than the Castle Daventry's central keep. The ruins are located on the flanks of a large hill near Connor's community in Daventry town.
Background
The ruins are bordered on one side by a moat, and it is the ruins of a castle that predates Castle Daventry, Edward's castle, the castle that Graham and Valanice currently live in.
While it's unclear on how old the castle actually is; The castle appears to have been in use during perhaps the later half of his Edward's father's reign, and early period of Edward's reign, as it is said he built the current Castle Daventry as a wedding gift for his wife.[1] However the location of the Edward's castle dates back to first kings of Daventry, and a castle and the existing moat had been located in that site for thousands of years[2][3]. Portions of the keep which had been in use by his father and ancestors were still there when Edward built his castle, and were incorporated into his design (so it appears he rebuilt or renovated and expanded on the ruins of the older castle).
It is not clear if the Castlekeep Ruins predate the moat and older portions of the restored castle, or if it came later. As such it would seem the Castlekeep Ruins if not the first castle (quickly replaced by one of Daventry's first king's for more spacious accommodations), it may be more recent than Daventry's oldest castle but older than Edward's rebuilt castle.
A hero of Daventry from many years ago is buried in a tomb near the moat, across the drawbridge. Due to the nature of the unknown age of the castle it's not clear when James was buried there, was he buried in ancient times or later when Edward lived there. If so; did he die long before the kingdom's loss of the three treasures, or did he die during the border wars that marked Daventry's decline under Edward.
The castlekeep may have still been in use as a defensive outpost during the border wars, but was damaged and lost during one of the battles (perhaps explaining the damage to the walls and buildings and the broken gate). If so, James may be the hero who died during that battle. Edward honored him by burying him near the gates he defended. Following the wars Daventry's borders continued to shrink, and what was left of the kingdom reverted into wilderness filled monsters and evil magic users, and very few citizens. Most of the residents left the kingdom, the king became besieged behind the new castle's walls waiting for end to happen, for the time when they were finally conquered by outside forces (Graham's quest was their last hope). Or perhaps James was the last surviving defender of the castle before it was lost, and he was honored and buried near the ruins under Graham's reign in memory of his valiant service there.
During the great cataclysm the castle was taken over by Spriggans, including their leader. One of Daventry's citizens, a Writer, had been exploring the ruins, shortly before the the cataclysm and was turned to stone by the vile tempest. A strange magical device is located in the keep, and could be used to travel between locations in other lands by use of a Magic Map. Connor decided to search the ruins thoroughly.
Geography
The castle is protected by cliffs on one side (which overlook the community and valley below), a large rises on another side, and a moat and draw bridge guards its front.
The walls in current times show extensive damage, as does the front gate which is busted. Only the wooden drawbridge remains but no way of lifting it. Most of the castle's four towers on the outerwall are broken or collapsing. The outer wall crenelations are largely missing, but can be seen in drawings of the castlekeep.
The castle was small, having only about 2-3 rooms at one time and several hallways around the outer wall. One space which may have once been a room is located just off the courtyard to the left upon entering the castle, but the roof has long since rotted away (or was destroyed at some point), and the walls were crumbling. A staircase leads up to the castle walls and from there one can access another room in the keep, the floorboards are still in place albeit rotting away in places (allowing one to see into the room below). Little is left to ascertain the room's exact purpose but it may have been the castle's single bedchamber. Another set of stairs circles the keep up to parapet. It would seem at one time a large flag once flew above the castle from the keep.
The castle keep ruins hallways are protected by traps, which can be turned off by pulling chains inside of a couple of small hallways located in the front wall of the castle. The traps are to protect the third room of the castle, the room which may have been the castle's throne room. It is there behind a locked door (the key was hidden in Castle Daventry), a strange magical device (a magical teleportation circle) was hidden within the castle's walls. The fact that the ruins may have been in use within the previous century under Edward may explain why the key to the room was hidden in the present in the newer castle.
In the courtyard just under the stairs, a chest filled with treasure could be found hidden behind a strange magical false wall. Perhaps this represented the castlekeep's former treasury.
Just across the moat is James's Tomb, located in an awkward and unlikely place blocking much of the road to the castle, it likely was built much later time then the castlekeep, after it went into disuse. According to Conner it would seem he had only been gone for many years, not centuries.
Behind the scenes
There is a steep hill behind the castle which lies between the it and the pond. While it does look like a mountain this is probavly game mechanics. As the magic map artwork and overworld map only shows hills in the area. The same goes for the steep barrier cliffs that surround the entire level.
The man turned to stone in the castle is known is apparently a 'Writer' based on the description in the debug mode. The most famous writer in Daventry is Derek Karlavaegen (in the lore he is pretty much the only known professional writer in Daventry and elsewhere), but these may not be the same character.
In the game Connor describes them as the old castlekeep of Daventry, or it's described as the "Castle" in the debug mode.. The proper titles originate from the KQ:MOE hintbook.
According to Mark Seibert, MOE producer, the old castle keep are the ruins of a castle that predates the Castle Daventry from the previous games, and the Castle Daventry in the game was intended to be the same one seen throughout the series.
However, even though the main castles location and physical design is not necessarily consistent with all other sources. Note: in some ways the location of the castle on a hill is more consistent with KQ1 and KQ3 and game box art from early games, and possblyy Companion's descriptions than it is with later games. KQ5 is probably the most inconsistent portrayal. Only the throne room is unlike that seen in previous games.
Unrelated, but interesting is in the 1st and 2nd Edition, of King's Quest Companion, the An Encyclopedia of Daventry talks about secret passages that pass under Castle Daventry, Edward's castle, that lead to portals that lead to other parts of the world. This is somewhat similar to the portal idea in the secret passage inside the Old Castle Keep.
Coincidentally the front view of the crumbling castle somewhat resembles the view of Castle Daventry as seen in KQ1, with the moat passing in front of the ruins.
If the novels are taken into account for this castle there are two possible interpretations.
Either it must be pretty old indeed, and likely the first castle of Daventry. But was given up for a more spacious castle by one of the first king's of Daventry. As the moat and Moat monsters in the current castle are said to have been established by one of Daventry's early kings (and the keep has been in use in some form for many generations of Daventry's kings). In fact according to KQ4 Daventry has existed for thousands of years already, thus could make the old castlekeep at least a couple of thousand of years at least.
Alternatively Castle Daventry in particular the central keep, was the first castle but in time fell into disuse, and the king's built and moved into the Castlekeep instead. It is said that during Edward's reign he built the current castle for his new wife. Which suggests he actually built the rest of the castle on the location of the old, incorporating and restoring the keep and the moat into it's architecture. In this case it would seem it was likely Edward that brought the key to the new castle and hid in a slot it behind the paintings, and no one discovered it when the paintings were replaced with portraits of Graham and Valanice.
In the Al Lowe Interviews Rosella there is mention of a Royal Summer Palace, which would suggest there is other castles perhaps a Royal Winter Palace as well. Although Daventy's main castle is also used all year round. Perhaps the Castlekeep Ruins is an example of castles scattered throughout Daventry. Perhaps Daventry even had a defensive fortresses put up all over its borders at one time. We also do not know how and where the rest of the kingdom's nobles and knights live. As such it could be an example of the ruins of one of the more modest accommodations of a lesser nobility of the kingdom. Perhaps even Graham and his Father's old estate, which might explain the hidden key behind Graham's painting.
KQ9: Your Legacy Awaits introduces another fortress the Knight Theatre, a coliseum-like structure where the knights of Daventry trained in the past. Although this is not likely to be the same location, it also appears to be another defensive structure in kingdom.