It’s no secret that Colorado’s terrain can be a bit difficult to navigate. As a result, there are plenty of tunnels spread throughout the state allowing easier passage of mountains. From railroads to roads to old mining routes, here are a few of the tunnels we thought were worth talking about. Did we leave one off the list? Let us know in the comments below.

1.Eisenhower Tunnel

Located at an elevation of 11,158 feet, this 1.69-mile-long tunnel is a true feat of engineering. Consisting of two 40-foot-wide bores through the mountain (eastbound and westbound), the Eisenhower Tunnel is the longest mountain tunnel on the Interstate Highway System. Approximately 32,000 vehicles pass through it each day according to most recent data (2007), though this is now likely much higher considering Colorado’s growth. Here’s a fun fact: it’s route takes vehicles beneath the Continental Divide.

2. Gold Camp Road Tunnels

Found in North Cheyenne Cañon in Colorado Springs, the Gold Camp Road Tunnels are often said to be haunted, attracting apparitions and chilling ghost stories throughout the years. They’re accessible via Gold Camp Road, but only two of these tunnels remain open to vehicles. The third tunnel of this set of nine can be found on the walkable continuation of Gold Camp Road, but is barred-off due to rock fall risk.

3. Old Colorado City Tunnels

A trailing echo of Colorado Springs’ seedy past, tunnels beneath the nearby Old Colorado City area once bridged the gap between tasteful shops and a former red light district full of gambling halls, bars, and brothels. A quick search online will reveal photos of these tunnels, but they’re closed off to the public.

4. Midland Railroad Tunnels

Found just outside of Buena Vista on Chaffee County Road 371, the Midland Railroad Tunnels were once home to – wait for it – the Colorado Midland Railroad, which traveled between Colorado Springs, Leadville, and Aspen. While the railroad is gone, some of these tunnels remain, a few of which you can drive through.

5. Hanging Lake Tunnel

Named after a famous nearby attraction, the Hanging Lake Tunnel goes through the southern wall of Glenwood Canyon, leading to Glenwood Springs. Each bore is 4,000 feet long, completed in 1992 with the total project costing $490 million.

6. Moffat Tunnel

A railroad and water tunnel that cuts under the Continental Divide, Moffat tunnel first opened in 1928. It was the first rail connection Denver had through the mountains to the west.

7. Veterans Memorial Tunnels

Twin tunnels on I-70, these tunnels were renamed to honor veterans in April of 2015.

8. Alpine Tunnel

East of Pitkin, Colorado, this tunnel formerly housed a narrow-gauge railroad. According to the U.S. Forest Service, it is still the highest railroad tunnel in North America. It was built in 1882, but quickly closed in 1910 following minor damage.