tubechallenge.com

Yes, I've done Paris Metro, and Berlin, Brussels and Vienna. All take less time than London.

I'm not sure Paris would necessarily be cheaper than Berlin. I've just booked myself a flight out there for the middle of March and it came in at just under £50 return, including booking fees etc.,

If my memory serves me correctly, Paris would be a minimum of £58 return if we took the Eurostar, no?

As well as that, Berlin is still having a bit of a hangover price-wise from the days of the old-East, so accommodation isn't anywhere near as pricey as it can be in the usual Western capitals.

Spot on. Usually cheaper to get to Berlin, and hotels in Berlin can be a fair bit cheaper than Paris. And it's a better city!

I am also rather interested in this, although my German knowledge has taken a nose-dive recently.

I was chatting about this with Soup Dragon at the last R15 event and it does seem that, given the fact it's actually a remarkably cheap weekend away, there's some interest in this.

Something Soup Dragon and I were discussing was potential challenges. Clearly there's the scope for a Full Network Challenge as well as an R15.

I was wondering if anyone had any other ideas as to what might be possible. A 'Zone A Challenge' perhaps?

You can find the network map here (PDF file)

Another thought I had was perhaps doing something with the tram network.

You can find the tram map here (PDF again). Perhaps something with the MetroTram lines?

I have played about with the Paris and Berlin Metro ( U-Bahn). But didn't do anything official with it, This was last summer time Its a very good network to play about with and if you no the tricks in the network, then its good to do
If you need any advice come to me Neil