Flattop Mountain Trail, Historic hiking trail in Rocky Mountain National Park, Larimer County, United States.

Flattop Mountain Trail is a mountain path in Rocky Mountain National Park that begins at Bear Lake Trailhead. The route climbs through forested slopes and open meadows before reaching a wide, flat summit area with views across the Continental Divide.

The Flattop Mountain Trail, also called the Grand Trail or Big Trail, was built in 1925 in what became Rocky Mountain National Park. In 1940 the Civilian Conservation Corps rehabilitated it. It was listed on the National Register of Historic Places on September 27, 2007.

The trail's other names, Grand Trail and Big Trail, come from its role as a main route to Flattop Mountain's summit. It was listed on the National Register of Historic Places on September 27, 2007, recognizing its place in the park's early trail network.

Hikers should bring plenty of water and snacks and start early to find parking at the trailhead. The elevation gain and terrain require basic mountain hiking experience and sturdy footwear.

The summit's flat top offers rare views across both sides of the Continental Divide from an open plateau. From here, hikers can continue toward nearby peaks or glacier areas and explore the high-altitude landscape further.