Italy in late January is cold, quiet, and dramatically cheaper than summer. You get Rome, Florence, and Venice without elbowing through tour groups, and the espresso tastes just as good when you need a coat to drink it outside.
A solid two-week trip for two runs around $5400 once you factor in flights, trains, hotels, and meals. Spreading that cost out over time makes the upfront bill easier to handle, as long as you have a clear payoff plan.
Keep in mind that an intro rate is a strict deadline, not free money. If you have any balance left when the 18 months are up, the card's standard ongoing interest rate kicks in immediately on the remaining amount.