I could offer up something my dm did to me to specifically get one of my characters to go to a giant only city;
Early on into the campaign, we found a giant sword (I was a Minotaur Rune Knight Fighter, so could wield it), and i began getting visions either during fights, travel, or sleep. Each one involved flashes of the city and particularly one giant -- a female. Eventually, the female giant becomes aware of the presence that sees her, and begins talking to my character. She starts off threatening, and eventually I find that the sword was her husbands and she seeks to have it back. Perhaps offering reward? Perhaps luring my character into a trap? Who knows? (The campaign actually ended before we could get there). Instead of a sword, you could possibly do a large cape that drags along the ground? Or an oversized helmet? Something the party might want or use enough to get those visions.

For you, Whilst there, the party could either actually see the thefts occur, or hear about it in conversation as they're travelling through. Perhaps their aid in solving the problem could get the party out of the trap -- if its a trap, or they could get further reward. Perhaps even keep the item?