Most natural caves would have rough terrain, not a smooth floor. Try adding rocks, debris, and small cracks.

Here are some cracks to try, and some webs. all these are from the Dundjinni forums.

483_Cracks_shadow02_dbl-c.png1Cracks01e_dgw.pngCracks2_bg_dgw-a.pngCracks2_bg_dgw-d.pngCracks2_dgw-a.pngCracks_ERN-g.pngFloor_Crack01_kpl-h.pngWeb_SB-a.pngWeb_SB-b.pngWeb_SB-c.png