Formed from the erosion of gypsum the cave is roughly 10-15 metres long and about 10 metres wide. However, 5 metres of the width are the visible sections of the lake. To your right as you enter there is a small passageway. I have not been through it so I cannot give you any details. The cave is always cold and damp and the water is crystal clear (and very cold) provided there has not been rain recently. This is not the only gypsum cave in the area. Not surprising given how easy gypsum erodes. I will detail the Lost Brook Cave at a later date as well as other gypsum-related sites.
While small now my mother says that at one point long ago the surface of the lake was wide enough to skate on in winter. True enough the roof of the cave only comes to the waters surface and very well may hide a larger chamber. How
this change occurred comes down to either the roof lowering under the weight of the mountain (a scary proposition considering how fast it would've had to occur) or the water level rose by about 6 feet. It is also possible that the stories
about the cave have been distorted over time or that such a section of the cave was accessible at one time but is not any longer. Exploring the lake itself would take someone with scuba gear as the aforementioned coldness of the water and lack of headspace makes diving unprotected risky.
Correction: An early version of this post labelled the location of the Underground Lake as being in a Class II Protected Area. It is, in fact, a Class I. If you travel here without permission you may be subject to fines up to $600 if caught.
To get to the Underground Lake take the 114 out of Hillsborough going south until you reach the Albert Mines Road. Continue on this road for approximately 10 minutes. Keep an eye on the right hand side of the road. You will pass the
Albert Mines Baptist Church. You will also pass a gypsum quarry. It is the next dirt road on your right after this that you want to turn off onto. If you pass the Curryville United Church, you have gone too far. Once on the dirt road keep an eye on your left hand side. The first area you find where you can pull your car off the road is what you want. There is a fairly obvious trail leading from this pullover area so you shouldn't miss it.
Following this trail will lead to an occasionally used campsite beside a brook. Depending on the year there may or may not be a way across without getting your feet wet. Directly across from the campsite is a steep hill you will need to climb. A kind person may have left you a rope to hold onto. Either way it is slightly easier climbing just to the right. Follow the trail until you come to the incline leading into the mouth of the cave. Again, a rope may have
been left here to help you down. If not, consider whether you really want to go down as it may make you muddy getting back up.
1. Don't visit in winter or early spring. The risk of injury from falls is very high. Wait until the woods have dried out.
2. Don't attempt to cross the brook if the water is high.
3. Don't go alone.
4. Don't yell in the cave. While it is pretty stable tempting fate is a bad idea.
5. Go in the morning or at mid-day. Going in the evening is a good way to get lost.