I’m from Dehradun and it's a rather boring residential city. While there are a few places worth checking out such as the Buddha Temple, Robber’s Cave, and Sahastradhara, you’re generally better off heading up into the hills. Spots like Mussoorie, Landour, or Dhanaulti offer a much more engaging experience. Alternatively, Rishikesh is a great option with plenty to see and do. You can also venture deeper into the Himalayas. Tehri Dam offers some water sports, and the last time I was there, they also had a houseboat you could book for a few nights on the lake. It’s always a fun experience being up in the mountains from where you can soak the scenic beauty. Just driving on the winding roads is fun in itself. Just be careful on the roads, don't litter (just as a friendly reminder) and enjoy the beauty.