In the fourth level of the first pack, there is a cave with spikes. The exit is very difficult to get out of.
Go straight ahead until the edge and then jump while going right. Make sure not to jump too early. Then when you are high enough go left.
Getting killed by spikes or falling off are all risks.
"Spikes damage you. You have to be very careful to get to the portal!"
"Go right and at the edge jump continue right then when you are high enough go left into the portal."