London Jigsaw Puzzle

The pieces come from photos of London landmarks — the Eye, Big Ben, Buckingham Palace, the Tower — cut up like a standard jigsaw. You set how many pieces each row and column gets before starting, so the same photo can be a five-minute puzzle or a much longer one. A hint option is there if you get stuck on where a piece belongs, which becomes genuinely useful once you're past the easier piece counts.