Flame Butterfly

HUD description before collecting: Flame Butterfly (Rare Butterfly; +100 Bear Points): It's the rare Flame Butterfly in a rare moment where it's not on fire. +1 Trophy

menu description after collecting: Flame Butterfly: Extremely rare butterfly here.

The Flame Butterfly is a Den Trophy, and one of the four butterflies needed to win the achievement Rare Butterfly Hunt.

Location
The Flame Butterfly is in the Ancient Caves.

Go to the area of the Lake Platform which connects to Greenpeak Campgrounds. Ascend the large metal antenna which has fallen from the platform above. At the other end of this platform, drop down onto a walkway on the right. Follow this walkway all the way back, and you'll come to a room with a metal scaffold and a traffic cone. In the back of this room, there are two pieces of electrical equipment. To their left, there are two passages: an upper one, and a lower one. Crouch and follow the lower one. At the end, jump off (and try to land in the pond to avoid fall damage). You will find yourself in a shady, waterlogged area under the Lake Platform.

There's an entrance to the Ancient Caves at the other end of this area; go there. You'll fall down and splash into an undeground lake. Swim to the other end and climb onto dry land. Follow this passage back until you come to several wooden timbers across a deep chasm.

Crouch, and inch to the edge of the chasm, near the middle. Peek over the edge and look for a timber below, spanning the center of the chasm. Carefully drop down and land on that timber. You should now be able to see the Flame Butterfly on a ledge to the left. Drop down and grab it.