Sisters Rock is three rock towers, two on the edge of the ocean and one a sea stack just offshore. There are two separate turn-out parking areas near milepost 314 on US 101 in Curry County, Oregon. A trail on a repurposed rock-quarry road leads down toward the rocks and ocean, with side spurs to a crescent pocket beach to the north and another beach to the south. A cave broken into one of the rocks allows views down into a sea cave in the partially hollow monolith.
I don't find Sisters Rock on the list of parks at the Oregon State Parks web site. That's a surprise, because while it's barely developed as a park, this is a truly great public resource, and a fantastic spot to visit. There are many gorgeous stops along the Curry County coast, but you should not miss this one.
Sisters Rock is assigned Oregon beach access number 168
Pictures at Google Image Search.