The first unconventional entrance he used was a boulder. He was very surprised when he had to use the large boulder as an entrance into the secret realm.
Apparently, the boulder was in a place where space was aligned between the main world and the secret realm. All he needed to do in order to enter the secret realm was to push the boulder with full force.
He had to use full force to move the boulder. If he only touched the boulder and didn't use full force to move it, he wouldn't be able to enter the secret realm.
He had to mean to move the boulder and have the strength to move it. Once the boulder is moved, space around it shifts, and the people around the boulder will be transported into the secret realm.
When that had happened, Arthur found himself in the secret realm attempting to push the boulder. If he pushed it again, he would be transported out of the secret realm.
