Numerous points of interest, I conduct my students open water training dives on one of the mounds or rock. Check out Rock Lake Research Society, google it-give ya some interesting background. :)
Mostly a boat dive lake, vis is great early and late season, through the ice is excellent. Three boat launch sites, or talk to mstrdvr, he could be talked into taking you for a dive. :)
Bottom composition varies, rock on the mounds/pyramids with muck off of the mounds.