This week 10 epic quest requires you to build special sandcastles.

This is possible at 2 locations. The first is north of Dirty Docks. There is an area on the beach where building 3 sandcastles is possible. The second location is south west of Holly Hedges.

You will see an outline of a sandcastle and when you approach it will alert you that you can build it. Just build all 3 in whatever location you go to and the quest will unlock.

Maps with both locations are shown below.

Map credit to fortnite.gg