If you go to only one sight, make it Fuerte de San Miguel and Museo Arqueológico de Campeche (Av. Escencia s/n, 9 a.m.–7:30 p.m. Tues.–Sun., US$2.75), about 2.5 kilometers (1.6 miles) south of the city center [1]. Built in the 18th century, the fort sits atop a large hill and includes a moat, drawbridge, and a breathtaking view of the Gulf.
The museum here is the real highlight though, housing a truly fantastic collection of Maya artifacts from around the state, including several pieces from the ruins at Isla Jaina [2], six spectacular jade funeral masks found at Calakmul [3], and urns decorated with tapirs, monkeys, and turtles from Río Bec [4].
Signage is in Spanish and English; look for the cardboard information sheets in each exhibit hall. If using public transportation, take a “Playa Bonita/Lerma” bus in front of the post office (US$0.35). The bus will drop you off at the turnoff to the fort, which is about another 500 meters (0.3 miles) up a steep hill.
Below the Fuerte de San Miguel is the Batería de San Luis (8 a.m.–6 p.m. daily, free), a small fortification that is empty save one exhibit on Captain Pedro Sáinz de Baranda y Borreiro, a native of Campeche and naval commander who in 1835 became the governor of Yucatán.
On the other side of town, the Reducto de San José El Alto (Av. Francisco Morazán s/n, 8 a.m.–8 p.m. Tues.–Sun., US$2) is a well-renovated fort complete with cannons, thick walls, and a spectacular view of the Gulf of Mexico. It also houses the small Museo de Armas y Barcos, a maritime and weaponry museum where you’ll find model ships, 18th-century weapons, and a few other colonial-era artifacts. Explanations in Spanish only. You’ll need a car or taxi to get there, and even so it’s easy to get lost.
Links:
[1] http://www.moon.com/destinations/cancun-the-yucatan/the-state-campeche/campeche-city/sights/city-center
[2] http://www.moon.com/destinations/cancun-the-yucatan/the-state-campeche/ruins-near-campeche-city/isla-jaina
[3] http://www.moon.com/destinations/cancun-the-yucatan/the-state-campeche/rio-bec-region/calakmul-archaeological-zone
[4] http://www.moon.com/destinations/cancun-the-yucatan/the-state-campeche/rio-bec-region/rio-bec-archaeological-zone