Ravensburger Krypt Inside The Riemann Sphere Jigsaw Puzzle Challenge (654-Piece) High quality components  Ravensburgers jigsaw puzzles for adults will bowl you over with premium quality, in terms of both content and material. Precision fit  No matter how large or small our puzzles, each is precision made so that every piece fits perfectly. Every piece is unique  None of the frustrations you find with other puzzle brands. With Ravensburger, every individual piece has a completely unique shape. Softclick technology  Individual pieces are so precisely made that you can actually hear a soft click when you fit a piece into the correct place. Long term quality - Ravensburger has been making products for the hand, head, and heart for over 130 years.