Fifteen miles south of Yachats is an enormous sea grotto that's home to hundreds of Steller sea lions. An elevator descends 208ft to a dark interpretive center, and a caged-off observation area lets you watch (and smell) the sea lions jockeying for the best seat on the rocks. From late September to November there are no sea lions in the cave.
Kids in particular will love this stop. There are lots of interesting coastal birds to look for here as well.