I tried the buildingtest1R scenario and could enter all of the buildings (both floors of the 2 story structures too).
I have Windows 7 Home Premium 64bit SP1, NVIDIA GTX670 (running 335.23), i5 2500K & 16GB RAM.
Display size: Desktop (1920 x 1080 60 Hz)
Model quality: Best
Texture quality: Best
High Priority process: Off
NVIDIA 3D Settings:
Anisotropic filtering: 16x
AA FXAA: Off
AA Gamma correction: On
AA Mode: Application controlled
AA Transparency: 8x (supersample)
Max pre-rendered frames: Application controlled
Texture filtering - Antistropic Sample Optimisation: Off
Texture filtering - Negative LOD Bias: Clamp
Texture filtering - Quality: Quality
Texture filtering - Trilinear Optimisation: On
Threaded optimisation: Auto
Triple buffering: Off
V-sync: Use application setting
Not sure if that helps or just adds to the confusion!