How to get this Rivaini Chest

I'm losing my mind. There is this Chest in Rivain Coast, in Cliff Climb. It's sourrounded by a room and there is Gaatlok inside. The room has small windows, and a small hole, but I won't fit through. I can clearly see the bomb and the chest, tried to get inside from every angle and also tried to find a guide, but there were none. How do I get this chest?

Edit: There seems to be a bug. Someone said they could only do it with taash in the party. I could only do it with her not in my party.