Narnia. Except that some things would be greatly missed (word processing programs, cameras, TLC... 😉 ).
WYR spend the day with Jill or with (post-VDT) Eustace?
Eustace. 🙂
WYR be captured by Telmarines or Calormenes?
Telmarines...
WYR have a Talking Bear or a Centaur for a roommate?
Visit the Islands, assuming Pug is out of business.
WYR have a Narnian painting or tapestry?
Definitely a Narnian painting,
WYR understand politics or be able to walk through the Professor's house once?
(*snerk*) Tour Diggs' house all the way!!!
WYR watch Father Christmas deliver the Beavers' gifts or the fixings for the Christmas dinner Jadis interrupted?
HAHAHA Good one, but I would MUCH rather see Father Christmas deliver the gifts. 🙂
WYR be able to play your favorite musical instrument better than anyone else on earth or stand next to Lucy, Edmond, Eustice, and Caspian at the edge of Aslan's Country?
Oh, definitely the latter. Because how cool would that be?
WYR learn metalworking from a Dwarf or woodworking from a Faun?
Augh, that's tough. ...Centaur? It seems like a more prestigious experience.
WYR swim with the mermaids or fly on Fledge?
Swim with mermaids.
WYR learn to play a Narnian game or to make a traditional (and very specifically) Narnian dish?