Iceland in May or September gives you the best of both worlds: fewer crowds at the major waterfalls and a real shot at catching the northern lights as the nights get longer. You get crisp air, quieter roads around the Ring Road, and steaming hot springs that feel even better when the weather has some bite to it.
A typical trip runs about $3400 once you factor in flights, a car rental, and places to stay. Spreading that cost out over time makes the upfront hit easier to swallow, but you need a solid plan for how you are going to pay it off before the bill comes due.
That 0% window is a deadline, not free money. If you still have a balance left when the 18 months are up, standard interest kicks in on whatever is left over.