I know it doesn't seem like summer yet, but I'm getting started a bit early this year with Somerville Open Studios.
An Open Studio event starts with a map, like this one. The dots on the map are artist studios (often just an apartment with a lot of art and an artist at work inside) which are open to the public for the duration of the show. Find a part of the the map you'd like to explore, and spend an afternoon walking between studios. It's a rare opportunity to see artwork in progress, instead of just finished works.
Since a lot of local artists don't maintain a dedicated studio space several restaurants and other venues are allowing artists to set up for the day in their show spaces. I'll be doing this at The Burren in their large back room which is #15 on the map. I and some other people will be there from 12 noon - 6pm on Saturday and Sunday. Stop in, have a drink, and buy some pretty things if the spirit (or the spirits) move you.