Zamrzlá lod' Kapitána Flinta

This may be the best book in the Swallows and Amazons series, which means that it might be the best children's book ever written. The Swallows and Amazons are exploring the Arctic (the area around the lake) during winter vacation when they meet Dick and Dorothea Callum, staying at a farm on the lakeside. Skating, signalling, exploring, ice-boating, astronomy, everything a kid could ask for.