Looks like this never-ending comic might finally be drawing to a close! They want to go see where the water is coming from, so off to pack some bags! Quite a long way we have come from the original tiny sandcastle.

To see the thing beginning to end (well, beginning to present perhaps) I suggest you check out xkcd.aubronwood.com - it lets you set your scroll speed, or if you just want to cut to the chase, hit the left arrow once the page comes up to go to the latest panels.