Cobá is a large set of ruins located about 50 miles east of Chichen Itza and about 30 miles northwest of the city of Tulum, with which it is connected by a modern road. During the peak of its civilization Coba is estimated to have had about 50,000 residents and extends over about 30 square miles. It is open daily, and there is a small entrance fee of about $10.
Coba itself is a huge, undeveloped archaeological site deep in the jungle, however, there is a large cleared area of major structures connected by roads and pathways. Temperatures are usually hot and humidity is often very high. There are the usual facilities including parking, gift shop, guide service, etc.
You can drive or take the ADO bus to Cobá from Tulum, Cancun or Playa del Carmen. Bus service leaves these cities in the morning and returns in the afternoon. The buses stop at a local restaurant, and it is a short walk from there to the ruins site. Just continue down the same road and make a left turn at the lake. It is easy. Of course, there are numerous all-inclusive tours originating from Cancun and other cities in the region. These include bus transportation, entrance, guided tour, meal, and at least one stop along the way.
This site is spread out, and the weather is usually hot and humid, so plan on a strenuous walk to see the structures. An easier method of getting around is to rent a bicycle (recommended) or hire a rickshaw and driver to drive you around. Guides are available.
The total site consists of a large set of ruins, some of which have been cleared from the jungle and restored . The Nohuch Mul pyramid is about 140 feet high, and is the tallest Mayan structure in the Yucatan and the second highest in the whole Mayan world. There are several other buildings of interest including temples, an ancient gallery of carved stellae, an astronomical observatory, and a ball court. The stellae are large slabs of stone upon which are carved artwork and hieroglyphics.
It is permissible to climb to the top of the pyramid, but it is a strenuous climb up a set of steep stone stairs, not always smooth climbing. There is a guide rope up the center of the stairs, but the climb is not for faint of heart. At the top is a small temple and a great view of the surrounding forest. The trip back down is harder because you are looking down. The top can be crowded with tourists, and quite hot in the middle of the day.
There are a few locations throughout the park where much needed refreshments are available, and also some shops and restaurants just outside the park. Wear sturdy shoes, a hat and insect repellent. Drink lots of water.