To the Basement!
Celerity would let Lina cover the ground floor, and mitigate the apparently space warping nature of the building as she breezes through. Without Celerity, Lina would get lost on the ground level where rooms seem to blur into one. With Celerity she has to criss-cross her path - but doing so does help Aaron as he follows behind.
For purposes of narration, I'm assuming the Celerity gets activated.
Lina finds the ground floor is as ruined as the upper floor - perhaps even more derelict. Certainly, she finds mouldering piles where once there was a squat - some years ago given the decay and dust that covers everything. The air is thick, too; thicker now than before. Dust motes hang in the air and when disturbed, float as if in molasses. If it wasn't for the Daeva's speedy investigation, they pair of Kindred might well have blundered into whoever was drawing near the building - or else gotten completely lost in the maze-like layout of rooms.
The sound of water is stronger on the ground floor - echoing up from a large and now empty basement. There is no hidden lab or mysterious stores in the basement; there are no objects at all, not even a rag. There is only the fuse box of the building - old and bulky and rusted; so ravaged there should be no power to the building at all. The only other feature of note is a massive hole in the wall: a puncture right through the building's structure.
The hole leads to a tunnel - none too safe and in danger of collapsing on itself. The tunnel rings with the sound of water. Rushing water from a sewer or flood mitigation network.