David Stanley
Google
The Castillo de San Sebastian (1706) occupies a tiny island off Playa de La Caleta at the westernmost point of Cádiz, Spain. Its artillery was intended to protect the city from hostile ships approaching from the west. The castle is largely abandoned but still accessible to the public. The entrance is always open, inviting the curious to come in. It's on a small island off Playa de La Caleta, accessible via Paseo Fernando Quiñones. It's an interesting one-kilometer walk.