Going underground: Minnesota caves, tunnels and mines that you can visit now

"Many subterranean palaces are said to be found in Minnesota," wrote Swedish author Fredrika Bremer in her 1853 book, "The Homes of the New World." Some of these "palaces" today are open to the public. Several caves, tunnels, mines and other underground curiosities in the state are open for self-guided touring — at a time when most cave group tours and museums are closed indefinitely.

Certainly the best-known cave along the North Shore of Lake Superior is the Cave of Waves, featured on old postcards. The relentless waves have pounded away at rock joints, carving out sea caves in the rocky promontory that forms one side of Crystal Bay in Tettegouche State Park. The adventurous can safely visit the caves by kayak; local outfitters can help.

A short hike along the scenic Brule River, flowing through Judge C.R. Magney State Park near Grand Marais, leads to the famous Devil's Kettle. There, half of the river seems to vanish as it cascades into a 50-foot-deep pothole in solid bedrock. While long dubbed a mystery, even by the Smithsonian, the vanishing water is only an optical illusion, as was proved by careful stream-gauging by the DNR in 2016. The water does not enter a secret passage, but rather rejoins the Brule River in the immediate vicinity.

A flashlight is optional for safely traversing the 469-foot length of the Ely's Peak Tunnel, because standing in the middle, you can see both entrances. Dug out of basalt, a dark volcanic rock, the tunnel was carved in the late 19th century. The Duluth, Winnipeg and Pacific Railway used the line until abandoning it in the 1970s. The former railroad bed is now a recreational trail linking to the Willard Munger State Trail and the Superior Hiking Trail on the outskirts of Duluth.

Miners have excavated more than 800 million tons of iron ore from the Hull-Rust-Mahoning Mine over more than a century. Named a National Historic Landmark in 1966, the world's biggest open pit iron ore mine is more than three miles long and two miles wide. It grew as many separate mines coalesced into the "Grand Canyon of the North," engulfing part of the town of Hibbing in the process. This enormous, terraced pit — and the miners who worked it — helped the nation win two world wars. Looking out over the mammoth hole from the edge of Hibbing, you can grasp its importance. Giant mining equipment is available at the overlook to explore.

Fillmore County is the heart of southeast Minnesota's cave country. The entrance to Goliath's Cave, at the bottom of a sinkhole in Cherry Grove Blind Valley Scientific and Natural Area, is gated, and a research permit from the DNR is required to enter. But you can get a good feel for the karst (limestone) landscape just by walking around on the surface. The cave floods to the ceiling during wet weather. The Minnesota Cave Preserve drilled its own entrance to Goliath Cave in 2004. An award-winning 2009 book, "Opening Goliath," was written about this cave and the wild passions it inflamed among warring landowners.

In Whitewater State Park, a rocky pinnacle juts skyward. Hike to this pinnacle and crawl into a cave at its base. Chimney Rock Cave features natural windows overlooking the valley and is large enough for an adult to sit up. Children enjoy the fort-like appearance of the cave, but the sharp drop-offs beneath the windows make adult supervision a must.

This one sits high atop a sandstone ridge near the town of Reno, Minn., overlooking Minnesota, Iowa and Wisconsin. The cave's walls are vertically fluted where rainwater has seeped through the caprock over time, widening the rock joints and washing out the void space below. But the small cave was well known for the prehistoric petroglyphs carved in its walls, especially the famous "Reno face," first documented in 1888. Subsequent surveys found them effaced by modern graffiti. Natural bays with seats and windows, present where the elements have gnawed through the walls, allow you to gaze off into the distance. Perhaps someone was sitting in that same natural seat just after the last Ice Age, looking out as a modern visitor would.

Located in the Richard J. Dorer Memorial Hardwood State Forest, the trail begins at the Reno Horse Campground on State Forest Road 540. The hike from the campground to the cave is about a mile with an elevation gain of several hundred feet, but the site is not well marked.

Greg Brick is the co-author, with Doris Green, of "Minnesota Underground" (henschelhausbooks.com).