Shetland was part of the Scandinavian world from the late first millennium until 1469, when the islands became transferred to Scotland and as a result most of the place names around the bay and some of its present-day culture are of Norse origin.

[4] 5 kilometres (3.1 mi) southwest from there is the inhabited island of Papa Stour with its outliers Brei Holm, Fogla Skerry and Maiden Stack.

This narrow neck of land joins the Northmavine peninsula to the rest of the Mainland Shetland and separates St Magnus Bay from Sullom Voe, an arm of the North Sea by only just over 90 metres (295 ft) at its narrowest point.

The most northerly waters of the bay are reached at the head of Ura Firth in Northmavine, of which Hamar Voe is an extension to the east.

The power of the ocean storms is displayed at Grind o Da Navir, a large amphitheatre just north of the Eshaness light that opens out through a breach in the cliffs.

[11] The base is a platform of Lewisian gneiss overlain with the East Mainland Succession of metamorphic rock, some of Dalriadan age.

[2] Initially the idea was proposed by A. W. Sharp purely on the basis of the bay's circular shape and he estimated that the original crater had a diameter of 11 kilometres (6.8 mi).

Subsequently bathymetric imaging suggests that there is an enclosing under sea ridge on the west side of the bay, although no conclusive evidence has yet been produced of such an event.

[13] The bay was thus probably created by glacial action, with the more resistant igneous rocks now forming the surrounding coastal areas.

A significant amount of strike-slip movement is also indicated by the lack of metamorphism shown by the rocks to the west of the fault, where they are close to Devonian intrusions.

[18] The rocks on either side of the fault have moved 170 kilometres (110 mi) relative to one another with the western section transposed northward.

[11] West of the St. Magnus Bay Fault the rocks of Papa Stour and Esha Ness are Old Red Sandstone and lavas of Devonian age, which have produced spectacular cliffs at the latter location and numerous caves at the former and at nearby Brei Holm.

It is so-called because of the tiny house at its top, which said to have been built in the 14th century by Lord Þorvald Þoresson, in order to "preserve" his daughter from men.

[8] Swarbacks Minn was home to substantial naval operations during the First World War, and was the base for the 10th Cruiser Squadron of armed liners and destroyers that patrolled the northern seas.

[24] In 2008 Forewick Holm was declared by its occasional resident Stuart Hill (aka "Captain Calamity") to be the Crown Dependency of Forvik and thus an independently administered jurisdiction from the UK.