The Chinati Foundation

You need a guided tour to go into the hangars with the actual art. You can see the big boxes outside on your own but they're underwhelming in my humble non-artist opinion. The guides are really strict and not very enthusiastic but very knowledgeable and passionate about Judd. If you're in Marfa it's kind of mandatory to visit the Chinati but maybe keep your expectations low.

A true art oasis in the desert. This is a very large space with tons of art/installations so plan accordingly. You must book a tour to access any of the buildings. Tours vary in length dramatically and do sell out so make a reservation in advance.

Just outside Marfa, this is a really cool place to visit. I recommend you plan to spend a day here. Visit in the morning, then take a break (off site) for a relaxing lunch and return in the afrernoon. Definitely book a guide you will get so much more from the experience, our guides Shay and Alex were so knowledgeable, they added to the whole day. It can be very hot walking around so make sure you're well covered. The artwork is inspiring and well worth the effort of getting there.