The fruit of the Prickly Pear cactus is known as Tuna in Spanish. They range in colour from green to red and are about the size of a medium potato and are sold from wheelbarrows on footpaths all over Cusco.
You get about 3 or 4 tuna for 1 sole (that's about 35 cents) and they peel them for you directly into a plastic bag. Just watching them peeling the tuna is fun... The cut across the top and bottom, leaving just a little bit in tact, and the put a slice lengthways between the two cuts, and then fold the skin back in one movement - you then put your plastic bag up to grab the fruit.
Mum buying tuna for me to try
Here's a video of how it's done...
I also love how the lady just opens her apron pocket for the money to be dropped in.
I don't know how to describe the taste... It's sort of crunchy but soft (a bit like the way watermelon has a bit of crunch but more-so) and has lots of seeds through it and it's quite juicy too.