Castillo de San Andrés Tenerife

One side of this fort has collapsed, but the rest is still standing, so while it may not be that large or imposing, it's a significant chunk of surviving heritage in San Andrés. Dating to the early 18th century and constructed to protect Tenerife from pirates, the fortress played a role in the Battle of Santa Cruz de Tenerife (1797), the battle in which Horatio Nelson lost much of his right arm.