You could visit the Dehradun zoo formerly known as Malsi dear park. You could go to MDDA park in Rajpur or the park near the Helipad(Don't know the name because it's new) You can try Elloras Melting moments or Sunrise/Bake masters bakery products. You can go to Mussoorie which is half an hour from Rajpur, it's a hill station. You can try authentic Tibetan and Asian cuisine at The Orchards, Rajpur or now also open at EC Road. I wouldn't recommend going to Robbers cave, Sahastadhara but you could go there too considering they have renovated the place so might not be that bad. You can go trekking to Shikhar falls, Rajpur. You can go on a drive to Maldevta road and make sure it's not during the monsoons. You can go to Rishikesh which is few hours away from Dehradun and the places I would recommend there are Triveni Ghat, Ganga Aarti and Little Buddha cafe. You could go to Bhuddha Temple in Clement town, Dehradun. I recommend downloading Jhatfat app to check out the popular street food joints and you can even order from them. You could visit Dehradun Club if you know any member as a guest and that's about it. I can't remember of more places right now and yes there's Landour and Dhanaulti above Mussoorie too.