It's all in good fun for a great cause - but might be kiiiiind of shocking if you just stumbled upon it without the backstory - tomorrow (Saturday February 10th) is the annual 1 mile Cupid's Undie Run in Philly, a fundraiser for the Children's Tumor Foundation. It is what it sounds like - a bunch of people running around without pants on (but if that's not your thing, costumes are ok, too)
Registration is $40, and the event (including music and celebration) runs from noon-4pm, with the hub at World Cafe Live. More info/register here.