From Bulbapedia, the community-driven Pokémon encyclopedia.
The Vista Lighthouse (Japanese: シルベのとうだい Shirube Lighthouse) is a location in Sunyshore City, Sinnoh. The player can see the Sinnoh Pokémon League building if they look into the binoculars.
Unlike the lighthouse in Johto, this only has an elevator and an observation deck, not even any Trainers. However, it has a similarity in that it is the location in which the city's Gym Leader, Volkner, is found before appearing in the Gym.
Volkner, unlike Jasmine, however, is not caring for an ailing Pokémon, merely contemplating remaining a Gym Leader or going to the Pokémon League to challenge the Elite Four, since he has had no worthy challengers for a while.
The Vista Lighthouse is located on the far south east side of Sunyshore City. It was built to help guide ships and boats into Sunyshore's port, representing safety and protection to all Sailors.
It was built on a large rocky cliff face right beside the sea. It is a large lighthouse, but only one floor can be publicly accessed by people, the top floor, which is only accessible by a large elevator. Once on the top floor, people can see the views and even use the binoculars to see far and wide, even the Pokémon League building towering over a great waterfall. There are also seats where people can have a rest and take a break. At one point, the Sunyshore Gym Leader, Volkner can be found here by the player, before appearing in the Gym.