Kolima doesn't have much to offer at first, but it serves as a catalyst for several important events later on.
Kolima (Tret's Wrath)
After passing through the barricade, you will find Kolima waiting on the other side. Upon entering, a rather lengthy cutscene will take place, where the source of the town's curse and how your party can help to break it. Since everyone is currently a tree, there's not much to do here. Explore the town as you want, be sure to check all the barrels as usual, and you can also use Ivan's Mind Read to actually hear what the residents who have become trees are thinking. Also, when you attempt to exit the town, you will see a Venus Djinni trapped in someone's backyard. Approach the rear of this house and walk into it. You'll be taken into a back room with a hidden door. Climb down the ladder in here and go through a short dungeon-esque area until you find another ladder. Climb up and you'll find yourself in the backyard. Just talk to it and Granite will be added to your arsenal.
Kolima (After the restoration)
Once you've given Tret the Hermes' Water, everyone in Kolima will return to their human form. Now you can talk to everyone and check out the contents of the shops. You should also stop by the Bilibin Barricade and see the children you saved/doomed.