the more agriculture-dominated southern remained more rural in character. Due to economic, ethnic, and cultural differences between the northern and southern parts of the present-day Door County, arguments are sometimes started about the most appropriate place to draw the Door–Kewaunee line. Geography Caves and sinkholes A pit cave containing the skeletal remains of both present-day and pre-Columbian animals opens at the southern base of Brussels Hill. It is the deepest known pit cave and the fourth-longest known cave of any sort in Wisconsin. It was discovered by excavating three sinkholes in an extensive project. Hundreds of sinkholes in Door County have been found and marked on an electronic map. Most sinkholes on the peninsula are formed by gradual subsidence of material into the hole rather than a sudden collapse. Some are regularly filled by tilling or natural erosion, only to subside more due to meltwater or heavy rain. Many caves are found in the escarpment. One of them, Horseshoe Bay Cave, is Wisconsin's second-longest and contains a 45-foot-high underground waterfall. Horseshoe Bay Cave is home to rare invertebrates. Several tiny caves at Peninsula State Park are open and accessible to the public. Eagle Cave is larger but opens midway up the scarp face. Only one cave not formed by karst or lakeshore erosion has been discovered in Door County. It opens in the basement of a nursing home in Sturgeon Bay. High points Door County Structures on high points A tower on Brussels Hill is owned by the Wisconsin Public Service Corporation. Boyer Bluff Lighthouse is an 80 foot (24 meters) tall skeleton tower on , elevation 722 ft (220 meters) "The Mountain" at Mountain Park in Washington Island is the highest point on the island and has a lookout tower. Eagle Bluff Lighthouse on Eagle Bluff , elevation 597 ft (182 meters) Pottawatomie Light on Pottawatomie Point on Rock Island. A wind turbine project on the escarpment was completed in 1999. At the time the 30.5-acre (12.3-ha) Rosiere Wind Farm was the largest in the eastern United States. Other high points Deathdoor Bluff , elevation 728 ft (222 meters) Ellison Bluff , elevation 587 ft (179 meters) Mount Lowe , elevation 728 ft (222 meters) Sister Bluffs , elevation 581 ft (177 meters) Svens Bluff , elevation 633 ft (193 meters) Table Bluff , elevation 623 ft (190 meters) Certain other high points are currently unnamed Kewaunee County Cherneyville