Aside from Gettysburg, the only other historical site that comes to mind is Valley Forge but that’s about 25-30 minutes from Philly so doesn’t sound like what you’re looking for. Hawk Mountain is great for nature/hiking and it’s about 1.5 hours from Philly. So still not 2-3 hours away but that’s all you’ll get from someone who lives outside of Philly lol!