Tranquillity Park, Urban park in Downtown Houston, United States.

Tranquillity Park is a two-block municipal park in downtown Houston, built over a subterranean parking garage and completed in 1979 to the plan of Charles Tapley and Jeffrey Lunow. A sunken rectangular plaza of pale concrete holds three smooth green-tinged cylindrical columns on a raised platform, with steps and ramps leading down and a shallow water channel running through the lower part. Mounds and depressions across the grounds stand for the cratered lunar surface, and a rough beige-grey concrete wall carved with the words "Tranquillity Park" stands beside a brick walkway.

The park opened in 1979 to mark the tenth anniversary of the Apollo 11 Moon landing, which took place in 1969 on the Sea of Tranquility. That event directly shaped the park's name, design, and the symbols found throughout it.

Bronze plaques at the main entrance carry Neil Armstrong's first words from the Moon, "Houston, Tranquility Base here. The Eagle has landed," in 15 languages. The park's name keeps the British spelling "Tranquillity", unlike the Sea of Tranquility it commemorates. A replica of one of Armstrong's lunar footprints is displayed inside the park.

The park lies between Walker and Rusk Streets, west of Smith Street, with the federal courts building on one side and Houston City Hall on the other. It was built over a subterranean parking garage, so the walkways and mounds sit above the garage level. The sunken plaza with the fountain is reached by steps and ramps from the surrounding pavement.

The park's water fountain features tall stainless steel cylinders arranged in 32 levels that were designed to echo the booster stages of an Apollo rocket. Many visitors notice the water first and only later realize the cylinders are meant to represent a launch vehicle.