Suggestions for a South American city to spend a 2 day layover?

Heading to South America this August. My friend departs a couple days earlier than I need to, and I’m thinking of planning to travel to an extra city from our last destination (MEX) before I head home.
I enjoy nature, museums, exploring cool cities and doing random cool things (vague, I know). I’m mostly concerned with wanting to go somewhere where I’ll feel comfortable and safe exploring on my own in the daytime hours as I haven’t spent more than 12 hours solo travelling before. TYIA!

ETA: we will already have done Peru, Guatemala, Mexico City, and I will be coming back in January to spend time in Santiago!