You never really know what could be hiding underground.

From amazing restaurants to abandoned subway systems, there's a whole other world hiding beneath Ohio few people know about. The following are 8 incredible places you'll find hiding underground in Ohio. See how many you knew about and which ones surprised you:

1. Cincinnati's abandoned subway

Not many people are aware of the dark, lonely and long-forgotten subway beneath the streets of Cincinnati—the country’s longest abandoned subway system that never transported a single individual. Located under Central Parkway in downtown Cincinnati, (from Walnut Street to just south of Hopple Street,) sits the incomplete, eerie series of tunnels, which have been abandoned since 1928.

2. Ohio Caverns (West Liberty)

The Ohio Caverns were formed thousands of years ago when an underground river cut through ancient limestone and created vast rooms and passageways. Today, they're filled with crystal stalactites, stalagmites and other fascinating formations. There are several different tours you can take at Ohio Caverns, including a Natural Wonder Tour, Historic Tour, Limestone Tour and Tree Tour. You'll find the caverns at 2210 State Route 245 East, West Liberty, OH 43357.

3. Crystal Cave (Put-In-Bay)

Crystal Cave on South Bass Island lies 35 ft. below the surface and is about 12,000-15,000 years old. The cave is made up of celestite crystals ranging anywhere from 8 to 18 inches long. As you walk through it, you'll feel like you've entered another world. It's the world's largest celestite geode, making it one of the state's most unique attractions. Crystal Cave is located at 978 Catawba Avenue, Put-In-Bay, OH 43456.

4. Cleveland’s abandoned subway

Cleveland is also home to a lonely and long-forgotten subway system. The Detroit-Superior Bridge, (also known as the Veterans Memorial Bridge), is a 3,112 ft. long arch bridge over the Cuyahoga River, linking Detroit Avenue and Superior Avenue. When cars pass over this bridge, they’re also passing over a lower streetcar level that hasn’t been in operation since 1954.

5. Sotto (Cincinnati)

Hiding beneath East Sixth Street in the bustling city of Cincinnati is one of the most divine Italian dining experiences you can have in the state of Ohio. The atmosphere and decor are downright romantic, making Sotto the perfect date night destination when you want to really impress that special someone. You'll find it at 118 East Sixth St., Cincinnati, OH 45202.

6. Seneca Caverns (Bellevue)

Located in Bellevue, Ohio is another geographical wonder that was first discovered in 1872. When you venture to these caverns you will travel through "The Earth Crack" and view the Ole' Mist'ry River. You'll find Seneca Caverns at 15248 E Township Rd, 178, Bellevue, OH 44811.

7. Utopia's chapel

Once upon a time, the small unincorporated community Of Utopia was one of the "phalanxes" (or social communes) established in America in the mid-19th century. Utopia was founded in 1844 by Charles Fourier, a Frenchman who believed that the world was about to enter a 35,000-year period of peace. While the utopian society idea of the town failed, a spiritual group still held secret services in the town's underground chapel (pictured.) Today, along the banks of the Ohio River in Clermont County, you’ll find what some consider to be a ghost town, although the town is still home to some residents.

8. Olentangy Indian Caverns (Delaware)

History and geology blend at this unique attraction, which features caverns once used by the Wyandotte Indians. Formed by an underground river cutting through solid limestone rock, these caverns were formed millions of years ago, making them an exciting natural wonder to explore. Above ground, you can mine for gems, explore Frontier Town and even play mini golf at the Olentangy Indian Caverns. It's a great family day trip destination. Olentangy Indian Caverns is located at 1779 Home Rd., Delaware, OH 43015.

Did you know about all of these places? Which ones have you explored? Share your experiences with us!

For more unique caves to explore in Ohio, check out our previous article: The 9 Most Amazing Cave Adventures You Can Have In Ohio.