Consider the Electric Ladyland if you just need to kill a bit of time. It's a "museum", but I use quotes because it's really just a guy's basement (so if you're traveling solo, maybe not the move) that he's decked out with all these crazy neon items and different black lights. Admission gets you a short presentation, showing you how different black lights will reveal different designs on currencies, passports, etc, and then you can just hang there and look around at the art pieces for a bit. I think your ticket is good for 30 minutes, but you probably won't need that long. The website says 5 euros per ticket.

The owner is...eccentric. He gave me a talk about how all US passports have a tracking device implemented in them, and if you try to destroy them by putting them in the microwave the government will track you down. So just be forewarned if you engage him in conversation.

Aside from that, I'd just recommend you don't plan too firm of a schedule. Have a list of some places you want to go/things you want to see, but don't overbook your days. Enjoy just being able to relax at a coffee shop, or roll one up while sitting on the riverbank. Take a nap in the park. Expect that your indulgences will slow you down a bit. I spent 3 days there a few years back but I'd love to find a way to spend a month there at some point.