Gibraltar is a strange place. Take southern Spain, northern Africa, and England, and smash them all together on a rock 2.6 square miles. Literally, one minute we are in Spain, using Euros, everyone speaking Spanish, and the next, we cross through immigration, and everyone is speaking English with a British accent, and using pounds to purchase items like Cadbury and beans on toast. 
Then there are monkeys. Actual monkeys. Barbary macaques live all over the rock, and you see them everywhere outside the town center.
Since we are on such a tight budget, we elected to hike up the rock, instead of taking the cable car or bus, like most sane people. This turned out to be a great decision, as we saw a bunch of monkeys, and also got to climb to the very top of the rock after the roads and paths ended. The vertigo inducing shear drop at the top of the rock, providing views of Africa, was worth all the pain our legs endured to get there.
Along the way, we visited St Michael’s cave, an underground cave (stalactites and stalagmites), where concerts are occasionally played.
It probably would have been more enjoyable without the flashing colored lights and techno music reminiscent of clubs in Barcelona.
Another site was the great siege tunnels, which, impressively were dug by hand through the middle of the rock in the late 1700s.
Gibraltar doesn’t get much hype as a tourist destination, but we had an amazing time there. I don’t think we could have spent several days there (way too expensive, not a ton to do), but it was great as a day trip.
Beer of choice: Bushy’s Gibraltar Barbary beer (To be fair, this beer is actually brewed on the Isle of Man, but it uses hops grown on the rock. It’s the closest thing to a native beer we could find. And it was decent.)