Under the physics we understand, using talads description the planet would look something like this:
A&B: You would be pulled to the sides of the cave except if you were right in the middle, where you would float.
C: The water wouldnt \"fall\" either way, not unless the mass of the stalagtite or the patch under the lake was absolutely massive, i.e. some super dense material; osmium
D: people inside the stalagtite would be either pulled towards the surface (the ceiling), or the sides of the stalagtite if they had enough mass.
and finally E: the crystal would i imagine act like modern day fibre optics, refracting light at the angle of incidence into yliakum