The airport itself is almost ALWAYS the clearance limit. I've never had it where it's not, but it is possible. That's why it's smart to file your last waypoint as an IAF at your destination. That doesn't mean you have to shoot that approach. But it's on your flight plan as an IAF, and if you go lost comm you can go and hold there. But this also doesn't mean keep flying to the airport (which is your clearance limit) and do circles over the field. The term clearance limit just includes any type of clearance ATC may give you since you will ALWAYS have a clearance limit.