From Bulbapedia, the community-driven Pokémon encyclopedia.
is an anime
-exclusive location that appeared in Mystery at the Lighthouse
. It's the anime counterpart of Bill's Sea Cottage
. Like its counterpart, it appears to be somewhere near Cerulean City
Ash and co. first stumbled across the lighthouse after he captured his Krabby and disappeared. When Brock explained that Krabby was being sent to Professor Oak's laboratory, Ash immediately wanted to call him to see if Krabby made it safely. Spotting the lighthouse, the gang decided to trek there.
Once discovering Bill, he began to tell them about how there are countless Pokémon in the world. In fact, he mentioned to them about one Pokémon that he had been tracking for quite some time. That night, a giant Dragonite came close to the lighthouse.
However, Team Rocket decided to try and capture it. In attempting to do so, they scared it off, and it swam away from the lighthouse.
Although he was upset at not being able to discover more about the Pokémon, he was very excited that he had been able to see it, and told the gang to be on the lookout for more that had not been discovered.