Iceland was an island country on Earth off the coast of the European continent. A major city was Reykjavik, while other locations included Huallfiord and Tiornes, the nearby coastal islands of Rolsker, Flatey, and Lundey. (TNG-R: "The Neutral Zone", okudagram;Star Trek: Enterprise, opening credits)
In the Julian Bashir, Secret Agent holoprogram, Julian Bashir fell out of a dirigible over Iceland. Luckily, he was equipped with a parachute and a submarine was waiting for him. (DS9: "Our Man Bashir")
The map of Iceland containing several locations appeared in the Enterprise opening credits, and is sourced from Theatrum Orbis Terrarum, printed in 1570 and considered the first modern atlas.  The area seen is the eastern north coast of the island (Tiornes refering to what is now known as the Tjörnes peninsula). Of another label on the map, "Huallatursfiord", only the first few letters were seen.
At one point during the production of Star Trek, Iceland was considered as a filming location, though this did not come to pass.  For Star Trek Into Darkness, the backdrop of the planetoid Carol Marcus and Leonard McCoy examined an advanced long-range torpedo was created based on photos of a black rock beach in Iceland.  Production finally took place in full on the island, encompassing the exterior scenes set on Hima for the Discovery third-season premiere, "That Hope Is You, Part 1"