Davidsgja
Depth is the range from the top of the site to its usual maximum; "recommended cert" is the mainstream-agency level operators usually ask for, not a legal rule. Currents and visibility change daily, so treat everything here as planning ranges.
Davidsgja is Silfra's wilder sibling: a rift in the same lake, minus the queues, the platforms and some of the polish. The crack widens as it runs offshore into Thingvallavatn proper, and its water, lake-fed rather than purely spring-fed, trades a little clarity for the chance of meeting the lake's celebrated brown trout, which patrol the fissure like submarines in the blue-green light. Divers thread between boulders pinched in the cleft and pass sections where both walls fall away into shadow. Cold, quiet and slightly rough-edged, it suits those who want tectonic Iceland without the crowd choreography.
The moment you come for: Uncrowded rift diving, resident brown trout, open-lake atmosphere
Topography: A broad fissure running out into the open lake, with boulder jumbles and deep clefts
Entry: A walk over rough ground from the road on Thingvallavatn's eastern shore; entries are less groomed than Silfra's stairs.
Know before you splash
Hazards: Cold water, uneven shore entry, and changeable lake visibility after wind.
Conservation: Within the national park; the trout population is protected and not to be baited or harassed.
For photographers
Wide angle: ★★★★☆ · Macro: ★☆☆☆☆ (editors' 1–5 rating of what this site gives each style of shooting)