This offer is from Groupon.
Grim Philly has a booth at the Independence Visitor Center and offers tours of Philadelphia's underbelly from gangster hideouts to haunted halls.
There are a few different tours available, and they're all $20. That's up to a 65% savings.
You need a Groupon account if you don't have one. To get a Groupon account, you'll need to give out your e-mail address.