Great hiking and great winter weather, not much else.
Things that we enjoyed there: relaxing in empty pools and hot tubs, snowball fights at the top of Mt. San Jacinto after taking the tram up from the desert, the beautiful and unique scenery in Joshua Tree National Park, the short Andreas Canyon hike that was so popular we did it twice, the short Tahquitz Canyon hike to waterfall that we did early in the morning before it got hot and before anyone else was at the falls, driving around and seeing famous houses and unique architecture, the air museum (DS loves planes), Sunnylands historic house and gorgeous grounds, a small botanical garden downtown, walking the main strip especially during the Thursday night street festival, and the zoo.
There's also this hike that looks great, but we didn't have time to make it there:
https://www.alltrails.com/trail/us/california/ladder-canyon-and-painted-canyon-trail--4This should definitely keep you busy for a few days, and leave you wanting to come back for more.