I’ve taken a few short trips from Bangalore, and I feel Nandi Hills is one of the easiest options for a quick break. It works well if you leave early, enjoy the views, have breakfast, and return by evening.
If you have a full weekend, I personally like Chikmagalur and Coorg for a slower trip. The weather, hills, and coffee estates make them nice places to relax. Mysore is a good choice if you prefer sightseeing and history.
For something more active, Ramanagara and Savandurga are good for trekking and outdoor activities. I would choose the place based on how much travel time I’m comfortable with.