The Dragon's Den was built by a clan of Dragon-type masters. It is a cavern with an underground lake and a shrine to Dragon Pokémon. Many strong trainers can be found here, and the Dragon Clan's Master will give the player a Dratini if he/she answers correctly to his questions. Silver can also be found here.
Clair will come and reward the player with the Rising Badge and the TM DragonBreath after refusing to do so at the Gym.