Ohio holds some interesting pieces of local, national and even worldwide history. Sometimes, you just have to look a little closer to find them. The following are 14 hidden gems in Ohio that hold historic keys to the past.

1. Ghost Ship (Also known as the Circle Line V)

The 186-foot steam-engine yacht is more than a century old and was first launched in April of 1902, as The Celt, by a rich railroad executive. Since then, the ship has been renamed numerous times and owned by multiple individuals throughout its lifetime. While it actually came to Ohio from Kentucky, it currently sits in a small creek off of the Ohio River, about 25 miles from Cincinnati, according to Roadtrippers.com.

2. Kelleys Island Glacial Grooves Geological Preserve

Few people know that the largest accessible glacial grooves in the world can be found on Kelleys Island. They're an incredible sight to behold.

3. American Sign Museum (Cincinnati)

Discover America's largest collection of signs at this Cincinnati museum and observe decades of American pop culture.

4. Lustron houses (Whitehall)

Designed after World War II and made in Columbus for returning soldiers, these houses were impressively durable, yet inexpensive. Few are still in use or existence.

5. Newbury Airplane Boneyard

In Newbury, Ohio resident Walter Soplata hosted a collection of military aircraft from the 50s, 60s and 70s. The graveyard featured approximately 20 stray aircraft that Soplata collected from his scrapyard job in Cleveland, "junking thousands of warplane engines that were declared surplus," according to his son Wally Soplata in a November 2007 issue of Air and Space Magazine. Soplata used to open his property to the public, but in recent years the aircraft boneyard has been kept private. Today, it is unclear exactly what remains of the aircraft graveyard.

6. Pyramid Hill Sculpture Park and Museum (Hamilton)

This outdoor museum and sculpture park in Hamilton is every fine art enthusiast's dream come true. The park features a 10,000 square foot Ancient Sculpture Museum, which displays Egyptian, Greek, Roman and Etruscan sculptures that are thousands of years old.

7. 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.

8. Piatt Castles (West Liberty)

Located in Logan County near West Liberty are two chateaux style castles with Gothic design. This private, family-owned museum features more than 200 years of Ohio history.

9. Hopewell Culture National Historical Park (Chillicothe)

Mounds abound at Mound City Group in Ross County where you will find the largest collection of Hopewell culture burial mounds in eastern North America, as well as a museum that showcases the Hopewell culture.

10. Great Serpent Mound (Peebles)

The largest (and most strangely shaped) effigy mound in the world can be found right here in Ohio in Adams County. The 1,348 feet long uniquely shaped mound depicts a snake, with an oval shape at its head. Although no artifacts or written records were found near the mound to determine who built it, a nearby village site shows evidence of occupation by both the Adena and the later Fort Ancient Cultures. The original purpose of the mound remains a mystery, though there is some evidence for astronomical correlations, according to arcofappalachia.org.

11. The Arcade Cleveland

The Arcade Cleveland was one of the very first indoor shopping malls in the United States. Today, it’s an iconic landmark and a historic mall, featuring an array of shopping and dining establishments and the Hyatt Regency Hotel. Built in 1890 by the Detroit Bridge Co. at a cost of $867,000, this Victorian-era structure consists of two nine-story buildings, connected by a succession of arches with a glass skylight spanning more than 300 feet along four balconies.

12. 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.

13. Dennison Railroad Depot Museum

More than a million soldiers came through this historic railroad station on troop trains during World War II. It is now a National Historic Landmark.

14. The Adena Mansion and Gardens (Chillicothe)

Located in Chillicothe, (which was actually Ohio's first capital,) this 2,000-acre estate was once home to the sixth governor of Ohio and one of the state's first United States Senators, Thomas Worthington—who is also considered by many to be the father of Ohio and the Ohio-Erie Canal. (Fun fact: You can also find a beautiful view of The Great Seal of Ohio on the grounds of this site, pictured above.)

Did you know about all of these? What other historic gems are there in Ohio?