"Yes," Gaius says, still limp and languid in the bed. "I did. The place has hot running water, so all you need to do is to go to the watercloset off the side there, and see the spigot above the tub -- turn it so the water begins to run. But don't turn it all the way-- otherwise we'll get nothing but hot water and no cool to temper it, and it'll be burning hot if we get in. Ishgard has indoor plumbing, yes? So like that."

At least, he knows they have fountains and fonts and things like that-- so they must have running water, and knowing their chill country, boilers as well.