LairMistress, I love the idea of doing a tunnel with your ramp. I'd go with the entrance up the ramp idea as well. If you want to take the cheap and easy way out, you could always use tree branches scavenged from the yard and twist/zip tie them along the sides of the ramp so they arch up over the top and form a tunnel. Then you could add lots of creepy spiderwebs and dangling spiders hanging down. If you have access, a black light shining on the spiderwebs would make it glow purple in the dark. Pop in a big arrow sign pointing toward the tunnel with "Enter at your own risk" and you're good to go! Let us see the final product, whatever you come up, with when you're done.