Time machines haven't been invented (yet), so if you want to travel to the past, you have to seek out what remains of it. Luckily, North Dakota has a lot of historical sites that give you the perfect opportunity to peek into the history of the state and of nature. Here are 10 sites that hold a time capsule of history for you to explore that you can visit right here in the Peace Garden State.

1. Petrified Forest

Those short pillars coming up from the ground aren't just rocks - they are mineralized and fossilized bases of trees that used to grow there thousands of years ago. The Theodore Roosevelt National Park in North Dakota is home to one of the largest and last remaining petrified forests in North America. You can see these trees from the time of dinosaurs up close and personal by visiting the South Unit of the park. There is a hiking trail traversing the forest you can take and it's actually pretty awesome. You won't believe how huge they are - the picture barely conveys their size.

2. Fort Abraham Lincoln

This historical fort in Mandan once stood as a military outpost and has been preserved and restored to today. The famous Custer house is part of the fort; it was the part-time home to the famous Lt. Col. George Custer who, according to myth, still haunts it today. There is a ton of history to explore and experience at this fort, and a lot of events take place year round that you can take part in. If you haven't visited it before, you should definitely put it on your list!

3. On-A-Slant Indian Village

While you're in Fort Abraham Lincoln, stop by this village that captures what life was like hundreds of years ago with these houses. The On-A-Slant Village once housed the original Plains Indian tribe for which Mandan is named. It is a huge part of area history and a must visit if you want to learn more about the fascinating past of North Dakota.

4. Ronald Reagan Minuteman Missile Site

This historical site in Cooperstown is literally like a giant, underground time capsule straight from the Cold War. Above ground doesn't show much, but underneath the concrete is what once was a very powerful spot. The missile silo still remains and the launch control center are both visitable and pretty much untouched from how they were left. The offices still have computers from the 90s and the launch control panel, shown here, has a rotary phone. It really is a blast from the past and also a glimpse into the tensions of the Cold War.

5. Des Lacs National Wildlife Refuge

Take a look into the natural wildlife native to North Dakota at this wildlife refuge near Kenmare. If you're a fan of bird spotting, this should be on the top of your bucket list. Anyone can enjoy the gorgeous landscapes around the Des Lacs Lake left mostly untouched and see what it was like before most of the land in the state became developed. It's beautiful and perfect for nature lovers.

6. Bagg Bonanza Farm

In North Dakota's earliest days as a state, the land rush from the east resulted in places like the Bagg Bonanza Farm to spring up all over the place. Most fizzled out and disappeared after a while, but some held strong and were successful and later preserved, like this farm in Mooreton. The house and buildings are immaculately kept with many original furnishings and details; it looks like an original black and white photograph taken over half a century ago come to life in full color. Tours are available of the house, and they are well worth a visit. Bonanza farms were a huge part of North Dakota's history and this is one of few chances to see what they really were like.

7. Lewis & Clark Interpretive Center

The famous duo Lewis & Clark, early explorers of what is now the United States, spent more time in North Dakota than they did in any other state. The area fascinated them and they sent back a lot of their reports to the east about North Dakota. This interpretive center in Washburn looks into everything about the team, what they discovered here, and how they did during their journeys. It also is right by an extremely impressive view of the confluence where the Missouri River and the Yellowstone River meet.

8. Maltese Cross Cabin

Although this cabin has been pretty much everywhere because of its fame, its final resting place is right in the Theodore Roosevelt National Park. It sits not far from the original spot Teddy himself had it built upon so he could have a hunting cabin to rest in. The interior and exterior are pretty much exactly the same and give a glimpse into the tail ends of the 19th century and the life of one of the most influential presidents in US history. If you're going to be in the park, this is a perfect place to stop and see, too. You shouldn't miss it.

9. Fort Union Trading Post

What once was a highly trafficked trading post in the late early 19th century has today been reconstructed into the breathtaking Fort Union Trading Post near Williston. This place is loaded with history of the area and of early trading of furs and other goods found in the area. The huge fort is located right by the Missouri River and is as picturesque as you can get. It's beautiful to look at and full of information to learn, resulting in a great trip for anyone to take.

10. Hi-Line Bridge

At one point this was the longest raised railroad bridge for its height in the world and still is one of the top ones today. Not only is the impressively long bridge still in use; it also holds a lot more history than you may know. It was so important for freight and transport that at one point it had soldiers guarding it around the clock during both world wars. The bridge was constructed in 1907 and still remains standing today. Talk about sturdy! The bridge crosses the Sheyenne River in Valley City.

How many of these have you been to before? Have any you plan on going to or that we didn't include and would recommend? Let us know!