You'll be able to find Waterfall Arts; it's the building with a giant banner on it:
The banner was installed as part of SEESAW -- a collaborative show by Anna Hepler and Karen Gelardi (who is also my sister). This weekend, I went up to Belfast to participate in an artist workshop with them and help take down the show. Fortunately, the banner will stay up indefinitely, so if you are driving through midcoast Maine, you'll be able to find the building easily.
In case you didn't make it in person, here are some pictures of the show.