LotRO Summer Festival guide page 7: Summerfest
Continuing on with our tour, we take you to the Dwarven festival known as Summerfest. This takes place in Thorin's Hall, in the underground cave area. If you're not familiar with the layout of Thorin's Hall, you may find yourself lost initially. When you first enter the hall, run past the large statue into the next hall. Take a left towards the large waterfall, but as soon as you see stairs going down, take those. Descending into the underground area, you'll turn to your right and see an open room, whee the inn and festival area is located.
There is also a dance leader here for your Dwarven dance emotes, a fireworks vendor, a pipeweed vendor and a scavenger hunt NPC named Ambi. His quest is fairly easy, as most of the ingredients you'll need are in Thorin's Hall itself. The list of items he needs is in your inventory, so you will need to right-click that list and solve each of the riddles to find his items. There are no other special events in Thorin's Hall besides these. We're guessing the Dwarves are too busy sleeping... er, working to do much else.