Quick TXL tips.

The bathrooms that are signed when you enter the terminal at TXL are staffed by the notorious German tip-me-or-die matron (used to be about 50 pfennig, naturally increased to 50 euro cents), and are generally fairly dirty. The bathrooms on the main level (on the corners of the big octogon that TXL is) are free, and much nicer.

Although the roof is closed, you can climb the stairs on either side of the entrance for an 'observation' deck type experience. Often more interesting than the limited views out from the gates or the overpriced cafes.

The Berlin Transport (BVG) info. desks are probably the most helpful in Berlin, with all staff speaking excellent English that will help you buy the best and more cost-effective way of seeing the city via public transport.