I visited this WHS in December 2015. It is a good example of a fortified colonial town in the Carribean as much of the walls, bulwarks, bastions, ramparts are intact and the historic centre has not yet become a museum. The colourful houses go well with most of the tourists who are not thrilled by the fortifications and the bastions house interesting museums inside. The most noteworthy is definitely the one on Mayan Archaeology which has quite a remarkable collection of jade masks from Calakmul. The restoration of the bastions of San Carlos (in Els's picture) is a clear example of over-restoration in my opinion and therefore I'd recommend Fort San Miguel which is just a short distance by car, out of the historic centre and overlooking the Gulf of Mexico (pictured here). The catedral has just been restored too and worth a visit. In the middle of the square garden, just watch out for the UNESCO plaque which strangely enough has been placed on the floor (so you might be stepping on it without knowing, as I did the first time I visited!). I enjoyed my time here and although it is not one of the best WHS on the list, it was a pleasant break from the Mayan WHS I was visiting in Mexico and Guatemala.