Dehradun has various bike rental places. My travel partner chose the Royal Enfield to rent. Much to it, it was the most expensive bike that could be rented. It was INR 1200 per day whereas there were cheaper bikes available which were around INR 600 as well. The Royal Enfield however had its perks, it was really romantic and comfortable due to the long seat. We could also place our bags comfortably. We were roaming around in Dehradun for a day after that.
First we went to Robber's cave in the day. It was a swift ride, fast and amazing. The wind blew against our faces. Robber's cave is a nice place to explore and there is water. You have to walk through the water to reach the end of the cave. Be careful, you may slip against the pebbles. There is a shop for spare sandals outside.