You can go to Museum Affandi by taking Transjogja (please do search for info first) or you can take online transportation (for public transport option). Or if you want to take a motorcycle, i took around 20-30 minutes from Malioboro area.
If you love art, this museum is one of the must visit museum in Yogyakarta. To enter the museum, the entry fee is Rp50k (you'll get a free guide and a free souvenir coupon).
Here there are lots of collection of Mr. Affandi and his relatives (like his wife, daughter and son). And this museum is managed by their family. There is also a course for kids.
When you visit the museum, you'll visit 4 area. The first one is the room where the collection of Mr Affandi is saved. Afterward, the guide will take you to the graveyard of Mr. Affandi and his wife. The 2nd one is the collection for Mr. Affandi collaboration. The most interesting one is the one made by his friends (including Chairil Anwar)
After the 2n room, the guide will take you to the pool where there is a shark sculputure there and then the guide will bring you to the 3rd room. In this room, there is a video from Mr. Affandi in Netherlands (you can watch it if you're interested). Or you can enjoy the others artwork from Affandi's relatives (like his wife/kids).
The collection has more bright colors tone and i pretty like it.
Last but not lease, the guide take me to the atelier of the work. Here, there are some unfinished paintings, done by the grandson of Mr. Affandi. If you're lucky, you may be able to meet him in person
You can do the research about Mr. Affandi before visiting the museum so if you have any question, you can ask to the guide while you're here. Happy sightseeing !