There are several lakes near Villach and all of them are popular for water sports. However, if you plan a holiday there in summer and love swimming or windsurfing, remember that the water of these lakes is cold.
The lake with the warmest water in this area is the Faaker See. In fact it is not as deep as the other lakes and it is situated in a sunny position, so its water gets warmer in summer.
If you bring USD cash, make sure to have banknotes $50 or smaller. On weekends, when banks are closed, you can not change $100 bills at hotel receptions or railway stations.
Also, if arriving by train, check beforehand what station your train arrives at as many international trains do not arrive at the main railway station (Hauptbahnhof) but at Westbahnhof. You don't want to end up waiting at midnight in the middle of nowhere (and that's what Westbahnhof looks like!) before your friends realize your train is due at another station.
When walking in the mountains on small paths you have to be carefull. Sometimes paths are slippery or small stones fall down.