Minnie, one of my sows, did this once while I was poo picking and I had a such a heart attack! She's only 8 weeks and absolutely tiny, but she's constantly climbing on everything. Her favourite thing is to chill out on top of the pigloo like a meerkat, and she also likes jumping up onto their log tunnel. They've all got to be three times the size of her, but up she leaps. It's surprising how high she can jump! I'm always worried about her little legs.
I'm wanting to get them a stacked c&c cage in the future, but I'm terrified she'll climb out of it!