Everyone has heard of Red Rocks, so if you've never been there to check out the world class theater, it's worth the trip. There are also a couple of walking/hiking trails you can check out.
This is a good trail for people coming from lower elevation. Challenging, but doable, with great views!
If you want to take a bit of a drive, you can head to the Garden of the Gods. Colorado Springs is about 1-1.5 hours South of Denver.
If you want to do some shopping, head to the outlets in Castle Rock. Still a bit South of the city, but great shopping.
There are multiple locations of this restaurant, but it's one of our favorite breakfast spots. Hint: try the cinnamon roll and share a sandwich with someone.
There are also a ton of breweries in this area. They're all pretty great so pick one!
Pretty cheap to take a tour of the distillery!
There are multiple locations of this arcade-bar around the city. Pick your choice! Lots of retro pinball/arcade games from which to choose!
There is a lot of cool street art and tons of breweries in this area. Check it out!
If you like tea, see if there are any tours operating while you're in town! Boulder is a short drive/bus ride away.
This is where the Colorado Avalanche (NHL) and the Denver Nuggets (NBA) play. If you like sports, check the schedules to see if there are any games.
There are multiple escape rooms in the city. Use the magical Google to figure out which one works best for you.
There are lots of ski resorts in Colorado that will still be open in March. A-Basin for example was still open on July 4 this year. I would suggest looking at the epic ski pass, as they offer a 4 pack that works at several resorts. It is significantly cheaper than resort prices, but I think it's only on available till mid November.
We've never been here, but have heard great things!