Guernsey is the second largest of the Channel Islands, an island group roughly north of Saint-Malo and west of the Cotentin Peninsula. It is not part of the United Kingdom, although defence and some aspects of international relations are managed by the UK. The island has a mixed British-Norman culture, although British cultural influence is stronger. The island has a local language known as Guernésiais, but the main language is English.

The island is part of the French Armorican Massif. The Southern Metamorphic Complex is older than the Northern Igneous Complex. As a result of the islands complex geological development with multiple phases of intrusion and deformation, the older northern complex is elevated above the geologically younger, southern. Guernsey has granite intrusions, but most of the island is composed of gneiss.

There are numerous mostly small sea caves along the coast. Especially on Sark, the caves are rather famous because the French author Victor Húgo lived some time on the island, and used the caves in his books. But actually those caves are very small and there is no outstanding cave worth listing. Nevertheless, there are boat trips visiting some of those nameless caves under the name Victor Húgo Caves. All listed underground sites are military structures of World War II, built during the German Occupation as part of the Atlantikwall.