+1 ^ for the Botero Museum. If you have any interest in 20th Century Modern art, this is a wonderful, and very manageable, museum. Botero's pieces are displayed in historical context with art of his contemporaries from the early and mid-20th Century. And the museum itself is set around a relaxing courtyard with a very atmospheric fountain and two stories of cool, shaded balconies.

Did not use taxis when I was there, and also avoided Uber due to things I'd read about (licensed) taxi drivers stopping Uber drivers. I just used a car arranged by my hotel, which was similar to any sedan car service in any American city. I also don't speak any Spanish so was looking for the most pain-free way to go.

Good luck and please report back about your one-day layover.