Randall Munroe (of xkcd) answering a question about theoretically boating on a lake of various liquid elements:
Liquid tungsten is really hard to work with.
Tungsten has the highest melting point of any element. This means there’s a lot we don’t know about its properties. The reason for this—and this may sound a little stupid—is that it’s hard to study, because we can’t find a container to hold it in. For almost any container, the material in the container will melt before the tungsten does.
The reason you’d quickly die if you rowed a boat through liquid nitrogen is also surprisingly interesting.
Randall’s “What If?” blog has become a must-read for me. Highly recommended if you’re the kind of geek to find stuff like this fascinating.