From Bulbapedia, the community-driven Pokémon encyclopedia.
(Japanese: 正樹 灯台 Masaki's Lighthouse
) 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 his friends 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 drive it off because it was coming closer to the place they were climbing up and thus potentially crush them as they intended to sneak into the lighthouse. In attempting to do so, they ended up blasted off, part of the lighthouse was damaged, 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.
Pokémon seen near Bill's Lighthouse