On Highway 87 from Rausu toward Aidomari, past the Makkausu Cave (closed), famous for its Hikarigoke moss, the entrance is right after the tunnel.

As the name suggests, this is a hilltop park where you can observe whales (Baird's beaked whales, sperm whales, minke whales, and killer whales) from the ground. There are only a few places in Japan, as well as Hokkaido, where whales can be observed from the ground.
From this observation deck, where you can see Kunashiri Island up close, you can watch the whales as they float to catch their breath on the surface of the sea.