The ruins at Cobá have two excellently preserved ballgame courts. Ballgame? Yes, apparently the Maya used to play a game resembling a kind of net-less volleyball or raquetball. Some historians say that the game was played as a substitute for warfare - as a sort of mediation - and that it may have involved sacrificing the defeated player. Ah well.
Another highlight in Cobá was the 42-meter pyramid Nohoch Mul.
The stairs are not in the best condition, and there is a sign saying 'climb at your own risk' in four languages. (I saw some people crawling up and down these stairs on all fours, but I found them to be quite harmless - some of the stairs at Huayna Picchu in Peru were much worse.) If you can make it to the top, however, there is a grand view to enjoy: jungle as far as the eye can see.
The white dot in the right half of the picture is another pyramid - the pyramid Xaibé that you can see in the picture below. It has a strangely rounded architecture, the first pyramid I've seen that had rounded corners. Since Cobá was abandoned only after the Spaniards came, I'm guessing the round corners may have been some kind of new architectural development that became popular only after Tikal and Palenque were no longer on the map. Unfortunately I couldn't find any mention of the construction date of Xaibé on the internet, so that's just my theory, nothing more.
All over Cobá, there were carved stelae, some in really good condition, others not so much. The better ones had signs next to them with drawings that showed what you were supposed to see. Just a little help to guide the eye, but amazingly effective to make sense of carvings affected by erosion.
Another thing I noticed again today was that it doesn't make sense to trust travel guides too much. For Cobá, it said to arrive early, before the masses of other tourists descend. It even suggested taking a 4:30am (!) bus from a city some 60km away. Well, I arrived at about 11am because it was convenient for me, and for much of my visit I had the site to myself. Low season be praised, of course, but the thing is that the other tourists read guidebooks as well. I'm guessing that the 4:30 bus carried more tourists than the five that were in my 10am bus. Sometimes it seems to be better to do the opposite of what the guidebook says ;-)
Later that night, I stood on my hostel's balcony to watch the fireworks. It's the Mexican independence day tomorrow, and the occasion seems to be valued highly enough that even a small town like Tulum - with less than 15.000 inhabitants - invests in big fireworks. I like fireworks, so I'm glad for any occasion that brings them about :)
