The best thing we saw was a stupid tourist who ignored the signs that warned not to take food out of the coffee bar at the primary ape site.

A Barbary ape jumped on her head and reached down over her shoulders to steal the food off her plate. He was a persistent devil, and though she did not have a scratch, she was not a happy tourist in the minute or so it took to get rid of him. Opinion was generally in favor of the ape.

It is a place about as utterly lacking in charm as any place we have ever been. All that is missing is poisonous snakes. But it is fascinating to look across to Africa and to see the amount of shipping that still passes through the Straits.

We thought it was a quirky little corner of the world. Not that we would return, but it did not make us throw up on our shoes either.

nytraveler - No, it's not "of course" they're monkeys, unless you're a primatologist which I rather doubt. They've been called apes since 1791.
Yes, Spain is much more interesting than Gib, but the OP will not be able to visit it from the Rock. The border crossing currently takes 6 hrs in both directions. I feel certain they'll visit other ports right in Spain.
The apes are wild animals, and people shouldn't expect them to be friendly. They need to take care.

Some not so smart people thimk they are the Barbary of Seville.

Most of the comments actually make me laugh a bit. It seems like Gibraltar is the worst place to be on the planet for some people here due to not being able to come along with the monos.

Tour or no tour should be depending on how you enjoy traveling the most. If I had a whole day to spend in Gib, I'd do everything on my own by walking. You could do something like this:

Get off the cruise and walk straight in the direction of Ocean Village. Enter on the pedestrian bridge to your left located at the end of the bus parking lot. That little exclusive residential area has a tiny marina with some fast food restaurants around. As it is en-route to the Main Street anyway, it's worth a peak for sure. If you feel like taking a look at the unique cross-the-airstrip-to-get-to-the-border situation, walk towards the Casino and take a right at the end of the boardwalk. It's only a five minutes' walk.

If not interested in the latter, leave Ocean Village just at the beginning of the "boardwalk" with the restaurants and bars to your left, cross the roundabout, enter casemates, grab a highly recommended smoothie at Joost little booth in the middle of the square and walk up Main Street. Take your time, as you are not in a hurry.

The cable car station (it's not a tram) is located at the southern end of the Main Street. On your way you'll pass the small Trafalgar Cemetery. You may want to pop into the Botanic Garden before or after. Also, have a look at Moorish Castle. Make sure to drink and eat before entering the Rock, as the monos know their business once bagpacks are being opened. If you show no fear and don't act a fool, you might well find one of them sitting on your shoulder or doing the high-five if they feel like it. Sit down someplace next to them on the road and enjoy watching the average tourists' behaviour and the monos' smart reactions. Make sure to see a guided-tour bus stopping next to one of the monos and enjoy the little show.

Visit the St. Michael's cave. However, in your shoes, I'd contact my travel agency to find out if they knew some locals to ask them to schedule a special cave tour by local guides in some other hidden caves, which are not accessible unless you know someone knowing the guide. You would be surprised to see all the beauties inside. Furthermore, you could actually take a swim in the lake inside of the Rock and learn so much more about the history of Gibraltar and its tunnel system. But well, that requires prior arrangements for sure. It's roughly a two hours tour and a real hidden gem in Gibraltar, most tourists have no clue about. Other than that, the St. Michael's Cave gives you a small idea of what's really inside the Rock.

The Siege Tunnels on the other side will offer you a decent view onto the mainland, the airport and have some interesting information to share, too.

Don't be too worried about the cable car. The last depature is scheduled for 19.45.

Oh, and in case you really enjoy hiking and are fit, you might find it interesting to climb up the Mediterranean Steps instead of taking the cable car.

I agree with MaloBalo.The rock is an interesting day trip!
What is your option, to stay on the cruise ship? On a clear day, you can see Africa. To walk/cross over the runway and visit the Spanish side is definitely not interesting.
It is fun to say you have actually been there!
Before you get back on board, do walk around and check out/compare the prices of things that interest you-it's duty free.