Maybe entering the portal takes as much energy as it would take to climb the long way? If the other end is on the moon you have to enter at 10km/s or something else you fall right back out. Warning: I am not responsible for damage caused by extreme tidal forces.
I caught a (wild) rabbit with a bucket.
It was running from a dog and fell into a window well. It got so panicked when I climbed down it almost made it out on it’s own (it was about 8 feet deep). So I set the opening of the bucket against the wall with a small gap, to give it somewhere to hide, then went to the other end of the window well, and it crawled right in when I approached again. Covered it with a towel and lifted it right on out.