Lone Star Geyser is off the beaten path and away from all the geyser basins accessible in Yellowstone National Park by car. It is an easy, flat hike up the old park road (now a bike path) along the Firehole River to the geyser. And not just any geyser--many people consider Lone Star almost as good as Old Faithful, but without the crowds or fences. Whether or not that is true, Lone Star is a spectacular geyser, with a large and dramatic base formation, that is well-worth the hike to see it.
The trail is a multi-use trail that has some sections of pavement, but it is mostly packed gravel. It is popular with bikers and hikers alike. The entire route is within a short distance of the river, and there are some nice meadow views along the way. But the highlight is the geyser, and there are some benches and a log book to record eruptions.
Lone Star consistently erupts about every three hours. There is usually a short minor eruption that last a few minutes and shoots about 40 feet above the cone. Then the geyser stops for about 20 minutes before the major eruption starts. The steam and water shoot about 40 to 50 feet for 20 to 30 minutes, finishing with a very loud steam eruption that is impressive for its power.
The challenge with Lone Star is the lack of information about eruption times. The geyser prediction apps and web sites do not cover it, and the only sources of information before embarking on the hike are the Old Faithful Visitor Center (who rely on hikers to report eruption times) and the occasional note left by another hiker at the trailhead noting the last eruption time. Neither of these can be relied upon, so catching an eruption comes down to a matter of luck most of the time.