The Castle of San Cristóbal (Spanish: Castillo de San Cristóbal) in Santa Cruz de Tenerife (Canary Islands, Spain) was the first fortification of significance on the island of Tenerife and the main defensive building on Santa Cruz Bay.

There remain only a few walls of the original building on display in a tunnel under the Plaza de España.

Today, the castle is a museum which houses the famous "Cañón Tigre" (Tiger Cannon), which shot a musketball to Rear-Admiral Horatio Nelson's right arm, which fractured his humerus bone in multiple places on July 25, 1797, the reason why he had his arm amputated.

One corner of the castle remains, and can be visited underneath the plaza, along with a small exhibition,[1] operated by Museos de Tenerife.

The bronze cannon was constructed in Seville in the 18th century, and is 3 metres (9.8 ft) long and weighs 2,000kg.