We were there in Sept, 2021- weren't sure what we would find, but wow! You are at 6,000 ft and have views of the magnificent glaciers and peaks.
Lots and lots and lots of hikes- of all ability levels.
Ride the Bernina Express to Tirano, Italy or Campocologno, Switzerland - and back. [We didnt cross the Italian border because of the covid restrictions at the time.] The scenery is some of the best in the world, and we actually enjoyed going out and back, as we didn't miss anything [total RT four hours.]
It's also mountain bike heaven. Many options for bike rentals, regular and e-bikes.
We had a hotel which gave us free passes to the lifts and the outdoor spa. The pool in the spa is 91 degrees year-round, and you can see the glacier from the pool. The ski lift goes to Alp Languard and the cogwheel train to Muragl peaks.
Use the Surovas "Stop by Request" train station, instead of the Pontresina train station. The Surovas station is in the forest, five minute walk into town, and is more quaint. The Pontresina train station requires a bus ride or an uphill walk into town.
We didn't really see much in the way of museums.
Enjoy your trip and this beautiful town! Safe travels!