miles and miles
A very long, unspecified distance. I've hiked miles and miles in these boots, and they're still in as good of shape as the day I bought them! I'd rather pay a little more for a hotel than be in some dinky B&B miles and miles from the city.
miles and miles
A considerable distance; also, a large interval, by far. For example, We drove for miles and miles before we saw a gas station, or She was miles and miles a better pianist than her brother: This usage was first recorded in 1889.