Thor [right] and Loki's [left] journey to Jotunheim, from "Norse Myths" by Kevin Crossley-Holland [Illustrated by Gillian McClure 1992]
Thor said summer was the open season and he announced his plan of making a journey east to Utgard and flexing himself against the giants. "However few they are," he said, "they are too many."
"In Utgard," said Loki, "you'll need sharp wits."
"Sharp wits," repeated Thor seriously.
"And yours are as blunt as your hammer," said Loki, winking at Thor. "Why not take me?"
Thor ignored the insult and accepted the offer. "Evil creature: good companion," he said.
Loki's eyes gleamed, now brown, now green, now indigo. His scarred lips twisted into a wolfish smile.
"Tomorrow, then," said Thor.
(I wish modern retellings more often would accept that the reason Odin and Thor often travelled with Loki once upon a time, was because they LIKED him. He wasn't always unpleasant or angry or malevolent, even if he was That Guy who kept people on their toes by having a giggle at their expense.)