1 Prof. Jones: {back within Dr Smith's earshot} Well, we should try to escape, I suppose. Let's start making a tunnel.
2 Monty: A tunnel?! Are you nuts, dad? It's 60 feet of hard-packed earth, and we'll emerge in the middle of Potsdamer Platz!
2 Ginny: He's right.
3 Prof. Jones: This is the problem with archaeology these days...
4 Prof. Jones: All that library research, but you can't handle a little digging!

Potsdamer Platz is the main square in the middle of Berlin, a stone's throw away from where Hitler hid in his bunker in the final moments of World War II. It's probably not a very safe place to be in the 1930s if you're on the run from the Nazis.

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2013-10-07 Rerun commentary: Since making this comic I have visited Berlin, however I did not actually go to Potsdamer Platz. It's a little bit away from the main tourist sites, and I wasn't there very long.

In fact, it may not entirely be accurate to say that Potsdamer Platz is the main square in Berlin. It's basically just a traffic intersection nowadays, not an open square where public gatherings can be held. Possibly better known is Pariser Platz, the square in front of the Brandenburg Gate. Certainly for tourists anyway.