Boney Island is a remote island near Wawanakwa which is known for being extremely dangerous. Its defining feature is the skull-shamed cliff on its side, hence the island's name. It is also home to the elusive woolly beavers, known to be carnivorous. Because it is so creepy and considered haunted, it is basically ensured that no one goes to this place to disturb the creatures there. This doesn't stop Chris from using it as a setting for certain challenges, though...
First mentioned in "Up the Creek" where Chris has the campers do a canoe race to the island, portage their canoes to a certain point to light a signal fire, then canoe back to Wawanakwa. He then mentions that there is a curse at Boney Island: if you take anything from the island, you will be cursed. Unfortunately, Sara didn't hear the warning due to listening to her MP3 player and wound up taking a tiki doll from the island. This started the "curse" where her team suffers a losing streek for three challenges until it was found out in "If You Can't Take the Heat".
After the merge, Chris has the remaining campers go back to the island AGAIN for another challenge in "The Boney Island Race", where three teams must canoe to the island, send a representative to run up the mountain to light a fire at the top, then hurry back to Wawanakwa (bringing the rep is optional).
Chris then sends the campers back for the third and final time in "Trial by Tri-Armed Triathlon", where it was revealed that Sara didn't return the tiki idol but instead broke it to pieces and flushed them down the septic tank. Each pair has to return their section to the cave before leaving.