One thing which is uncertain in your question is that whether the travel time is included or not in these two days?
Because If you even Opt to go the nearest Hill station like Rishikesh or Dehradun It would nearly take you around 5-6 Hours to reach depending upon the traffic. According to me you can go to Jaipur, as the highway to Jaipur (NH-8) From Delhi is quite clean and traffic free, so this way you would reach there early and can spend more time in the city. Other City you can go for two days can be Mussorrie which is around 35 kms away from Dehradun. Although it would take around 6-7 Hours to reach Mussorrie but then If you manage your time properly it can be a good choice to go. As there are quite few places to roam around there and also the weather is quite good. Hope this Helps!
Go to Alwar! i had been there last year with my boyfriend and trust me its one of the best place for weekend gateway..you can visit alwar fort..tiger sariska reserve..my 2 days trips were peaceful and memorable!