Key???

[DragonReborn]

After returning the Puzzle box to Antabolis he tells u he has a key if u come back. So when u go back he gives you this ancient dwemer key to the bottom of the dwemer ruin you just came from. Now, instead of reading something to tell me where the puzzle box is, i explored the entire ruins. Now there were some locks that i had to use spells to unlock. Eventually i got to a dead end where there was water. Does the key simply take me to this place where i already explored by unlocking using magic, or did i miss a place, or does the place that the key unlock only appear after recieving the key. Lastly, i unlocked several places using magic, so is the key the only way to open that door or is it possible that i already unlocked it. Finally, is the place cool or does it have any good items. Sorry if this is a bit difficult to understand.

[Marxist ßastard]

To my knowledge, the key does nothing special -- it just opens the locks that are now (For all practical purposes) nonexistant. If you want to expand upon this ruin, download the preview plugin for the Greater Dwemer Ruins project -- it's avaliable at Morrowind Summit.

[Malchik]

The key opens the lower levels leading to the deep ore passage. You have probably explored them already as Marxist says. IIRC there is only one locked door in the whole game that requires a key and that is in the Bloodmoon expansion.