Depends what you want to explore, if you are a mountain person, I suggest Manali or Ladakh, then again if you are a green mountain person, there are other options. For forests and greenery, you can go to Kerala. However Kashmir can offer you both but it'll be severely cold there so you'll have to consider that as well
In Karnataka try Uttara Kannada district that consists of Dandheli, Gokarna, Banavasi and Karwar. This place has everything from forest to mountain to beaches
Nature. It depends as in it could be mountains or Greenery. If it is mountains then you could go for Dharamshala, Mcleodganj. You could visit Spiti valley and enjoy the raw beauty. If Greenery on your mind then head to Kerala, Coonoor or Ooty as it would provide the best view of nature.
You can visit Bhandardara, a beautiful place to spend weekend in Maharashtra. In Bhandardara you can visit Umbrella Fall, Wisdom Dam, Randha Falls, Kalsubai Peak and many more places. If you are planning to come The Yash Resort is the best place to stay. There they have swiming pool and an awesome pool side cafe named YOLO Cafe.