This very popular tourist destination lies 19 miles (and a winding 40-minute drive) east of Cave Junction on Hwy 46. The Oregon Caves began as seafloor limestone deposits that were eventually hoisted into the Siskiyou Mountains. Molten rock forced its way up into rock faults to form marble, and acidified groundwater seeped through cracks to carve underground channels. Surface erosion eventually created an opening for air to enter, causing water to mineralize and create myriad formations, such as cave popcorn, pearls, moonmilk, classic pipe organs, columns and stalactites.
Guided tours let you explore the caves, but don't neglect the surrounding area. There's a handful of short nature trails, such as the 0.75-mile Cliff Nature Trail (offering good views) and the 3.3-mile Big Tree Trail (which loops through old-growth forest to a huge Douglas fir). Some fine wineries are also nearby.