The Lewis and Clark Expedition started in St. Louis and went west to the Pacific Ocean, stopping near present day Astoria. The Lewis and Clark National Park is situated at Fort Clatsop, where Lewis and Clark spent the winter of 1805-1806. This was the last encampment of the expedition before they headed back east.
There is a visitors center with displays about the expedition, a replica of Fort Clatsop, and a canoe landing on what is now called Lewis and Clark River (which feeds into the Columbia River). The park has jurisdiction over quite a few Lewis and Clark historic locations in the area, some of which I visited. Several state parks, both on the Washington and Oregon sides of the Columbia River, also preserve areas where Lewis and Clark explored.