There's no way to view this in-game as it has been deleted, and probably will not be added back into the game in the near future, as it has been removed from the game either partially or entirely.
Kars' Cave was a building that was meant to represent a castle and was located somewhere in the old map. However, this location has since been removed. Kars' Cave was a very well-made room, the architecture was similar to the design of castles. The entrance was a big hole with rocks on its side. There was a huge red carpet in the middle, and big pillars to hold the roof of this immense, unknown and mysterious building.
It is rumored that players would suddenly get teleported here, but nobody knows what caused it.
This place was formerly known as "DIO's Mansion" for some unknown reason.
This is one of the most mysterious places in the history of ABD.