I still yet to find all the hidden rooms. Such as the hidden summoning room in the Mage’s room. There are even hidden rooms that you can find. It has many rooms ranging from: main hall, armory, private quarters, poo, dojo, mage’s room and library to name some of the rooms. Showing off my display in cabinets in private quarters display However, to reach it you would either have to find its teleportation amulet or use the console code to give yourself the amulet.
It is set in its own dimension so it would not conflict with any other house mods I think there is one mod that gives it an exterior entrance but I cannot remember. The only house mod I use constantly in every Morrowind save game I have. When Rethan Manor became too small to house all of my trophies and ever-expanding soul gem collection, it was time to look for a house mod that had large spaces or at least display areas.
