Castle Mountain is a very rocky peak right outside of Estes Park, Colorado. It encompasses a whole ridge of castle like rock outcropings. Castle Mountain lies between the Black Canyon Creek and Fall River drainages, it is a kinda isolated peak so it provides awesome views of the town of Estes Park and the Lumpy Ridge. Have fun scrambling up this mountain and feel free to explore the rocky outcroppings that dot this mountain( watch out for mountain lions because the lumpy ridge area is the most comon site of Mountain lion encounters.
Travel to Estes Park, Colorado and park right on the right side of the road across from Castle Mountain Lodge( This is also a very good place to stay if you are visiting RMNP, but vacancies don't last long). The mountain is right across the road from Castle Mountain Lodge.
Although Castle Mountain is in RMNP very few rangers patrol so you can probably get away with some things but just follow RMNP rules.
There is no trail up this mountain but the route crosses some old dirt roads that you follow for a while. From Castle Mountain Lodge hike north up into the forest. Then you weave northwest up the steep slope. The easiest way to atain the actual summit is from the backside when you are facing it from the Lodge. The most important thing when hiking up this mountain is head up. I have climbed this mountain several times and I have never followed exactly the same path. The one way distance of this hike is .8 miles and the elevation gain is 1,134 feet.