Pennsylvania's main city is Philadelphia. In memory of Benjamin Franklin, The Franklin Institute Science Museum was built here and allows visitors the opportunity to understand computers, science, geography and astronomy. Greater Pittsburgh is highly populated and a hub for three rivers: the Monogahela, Allegheny and Ohio. Visitors interested in the colonial era will enjoy Pennsylvania Dutch Country. The town of Gettysburg is famous for the Battle of Gettysburg, which changed the course of U.S. history. The Allegheny National Forest spans across four counties and features many outdoor activities. The Pocono Mountains are located in northeastern Pennsylvania.