Across The Universe.
Anderson's narratives traverse multiple dimensions that sometimes converge:
a ship sails from Midgard to Jotunheim just as spaceships fly from Earth to everywhere else;
"Odin" is a god in heroic fantasy, a man in historical fiction and a time traveler in science fiction;
both Tir-nan-Og and Tau Zero involve time dilation;
the Roman Empire falls in historical fiction and the Terran Empire falls in a future history;
Merseians are like civilized trolls;
far future Artificial Intelligences are indistinguishable from gods to newly created human beings.
In case the Merseian-troll comparison is regarded as fanciful or inappropriate:
"...after his human guests had left, Ruethen and his staff had rolled out huge barrels of bitter ale and caroused like trolls for many hours..."
-Poul Anderson, Sir Dominic Flandry: The Last Knight Of Terra (New York, 2012), p. 193.