Útgarðr

Thor, in a rage, laid hold of his mallet and would have launched it at him, but Utgard-Loki had disappeared, and when Thor would have returned to the city to-destroy it, he found nothing around him but a verdant plain.

In Gylfaginning, Thor, Loki and their companions come toward noon to a city standing in the middle of a plain, so high that they must bend their necks right back to see its top. They find the gate barred, creep through the bars and enter a hall where men of huge size sit on benches. Their lord is Útgarða-Loki. He sets them contests: Loki eats against a man called Logi, Þjálfi races a young man called Hugi, Thor tries to drain a drinking horn, to lift a cat and to wrestle an old woman, Elli. They all lose.

Next morning, outside the gate, Útgarða-Loki tells Thor that he deceived them with illusions: Logi was fire, Hugi was thought, the horn’s other end reached the sea, the cat was the Midgard serpent and Elli was old age. When Thor, angry, raises his hammer, the king has vanished and, where the city stood, he finds only a green plain. Gylfaginning calls the whole account Thor’s journey to Jotunheim.

The city is therefore no ordinary place on a map, and the dot is a schematic marker in the Jotunheim region.

The name is glossed as outyards, the plural of Útgarðr, and appears in English as Utgard and similar forms. Wikipedia’s article is a short stub, so little scholarly debate is recorded, though it hedges with thought to be and variously attested.

It points to one difference between sources: Saxo Grammaticus's Gesta Danorum, from the 12th century, sets Útgarða-Loki in a putrid, indoor cave where he lived chained, which contrasts with the outdoor arenas of the rigged contests with Thor and Loki. Wikipedia’s article also mentions a version in which Utgard is the last of three worlds linked to Yggdrasil, home of external cosmic forces, but names no source for it.