Exploring the forts of Arrecife. Castillo de San Gabriel – the cannon, circa 1895, with riffling inside the barrel, to spin the bullet, to fire it straight. The ubiquitous volcanic stone is used in all the building work. Click for more history https://www.barcelo.com/guia-turismo/en/spain/lanzarote/things-to-do/castillo-de-san-gabriel/