Les toilettes sont au fond du couloir.
lay twah-let saw a oh faw dew koo-LWAAR. Click below to hear this.*
The bathroom is at the end of the hall.
In general, le fond means the bottom of something, like a cooking pot, or the ocean. And the end of something, like the earth or a road, is le bout.
Le couloir is the hall(way) or corridor. It runs horizontally, rather than vertically, but it has a fond nevertheless. It’s the deadend you run into where you can’t walk any farther.
And le couloir began its life literally as a place where something flows, because couler means to flow. Hopefully it’s just the foot traffic flowing, and nothing else. The movie we’ve been talking about is La Délicatesse, not The Titanic.
*Some mobile phones, such as Blackberries, won’t display the audio player. If no player appears, here’s an alternative link to the audio file:
Spk Frnch 
This phrase sounds like something from British English (or more likely, the British usage was taken from the French). In the UK, you frequently hear that such-and-such a place is at the “top of the road” or the “bottom of the lane” even if there’s no slope involved. It’s just the end nearest to, or farthest from, where the beginning seems to be. Don’t you just love language?! (Yes, of course you do or you wouldn’t be writing these posts.)
Love it! (The UK expression and language in general.)