Alaric was in the only completed area of his residence— the grand hall, or, entrance. He specifically told Mulder, in secret, to build it with plans that Ooze Town would one day become Ooze Kingdom. Thus, the project had been slow, expensive, and horribly grand.
'Even today I still sleep within a temporary residence...' Alaric sighed.
But, right now, Alaric had brought Destro Fen into his residence, because in one of the halls being built, there was a formation-driven door. After opening that door, one would be met with Alaric's personal treasury.
Or that's what he wanted them to believe. He filled it with all the treasures he could muster, just so that they wouldn't expect there to be a basement underneath it. Any possible thieves would have their curiosity sated after seeing the treasure.