Prickly pears are covered in larger spines, as well as smaller ones. The smaller ones are harder to see and hurt a bit more, so be careful while handling them. It may even be worth it to wear heavy gloves at first.
Slice off both ends of the prickly pear, then make a long slice from top to bottom.
Using a finger or butter knife, loosen the skin from the fruit. Grab a hold of it and peel it off. Transfer peeled prickly pears to a large stock pot, then add just enough water to cover them. Bring to a boil, then remove from heat and let steep for 30 minutes.
Mash the fruit with a potato masher, then strain to discard seeds. Strain it again through a cheesecloth if you'd like to get rid of the pulp as well.
Return the juice to the pot, but this time add the sugar. Bring it to a simmer and let it cook for 5 minutes, then turn off the heat and let it rest 15 minutes.
Taste it to make sure everything is as you'd like it, then juice the limes into the syrup. The bright citrus flavor will complement the prickly pear, as well as act as a preservative.
You should end up with between 2 and 4 cups of Homemade Prickly Pear syrup.