(See my amply noded tour of Howe Caverns for location, recommended dress, and tour quality comparison.)
A 10-minute drive from Howe Caverns, in Cobleskill, NY, these caves are much less extensive (45-minute tour), considerably less impressive, and a little less expensive to tour ($9.50 adult admission). The tone of the tour guide (and the web site, www.secretcaverns.com) is sarcastic and amateurish. (Howe Caverns is hard act to follow, I guess...)
The 85-foot entrance shaft was discovered in 1928 by two unfortunate cows belonging to farmer Leon Lawton. Word of the caverns reached the ears of engineer Roger Mallery, who was then employed in the reopening of Howe Caverns. Mallery commissioned some local youths to explore the caves, and purchased Lawton's property in 1929. Portions of the main passageway were excavated to make it safer and more accessible, and the fill was used to pave the passageway. After the addition of stairs at the entry, and electric lighting throughout, Mallery focused on preserving (what remained of) the natural state of the caverns.
The main attraction, at the deep end of the cavern tour, is a 100-foot waterfall, spray from which tends to make the tour a little foggy throughout. (Access beyond the waterfall involves crawling in 40-degree water through flooded passages.) Along the way, there are interesting domes and grottoes, but don't expect the guide to pause for long.
Skin oils will "kill" calcite formations, preventing minerals from continued deposit on surfaces. For this reason, the Howe tour prohibits touching of "live" formations. Secret Caverns has no such prohibition, and as a result, many formation surfaces are blackened and "dead". Many surfaces are muddy and/or slimy, water is cloudy, and there is a significant (300+) population of bats, so I mostly kept my hands in my pockets.