The best documentaries show us things we’ve never seen, or challenge common assumptions about a world we think we know. “Devil’s Playground” (7:30 p.m., Cinemax) does both.

I’ve always thought of the Amish as those quaint farmers who still ride horse and buggies, wear beards and avoid most modern conveniences to opt for a simpler life. In short, everything I know about them comes from watching Harrison Ford and Kelly McGillis make goo-goo eyes at each other in “Witness.”

“Devil’s Playground” focuses on the Amish practice of “Rumspringa,” which roughly translates as “running around.” Amish encourage their teen-agers to leave their sheltered world and experience the pleasures and temptations of the “English” world, or modern society. They hope that they will return to the fold after “Rumspringa,” ready to settle down, marry, raise kids and embrace the faith.

The teens profiled here do some serious running around. They appear to careen from the 18th-century world of hoop games and candlelight to the debauched excesses of “The Real World” in about 60 seconds flat. Teen-age boys are seen binge-drinking and smoking bongs. Girls discuss drugs, drinking and casual sex. It’s as if MTV bulldozed the Little House on the Prairie.

All of the teens interviewed here have a profound sense of their Amish identity and share an abiding belief in heaven and hell. Most of them fear that their sojourn among the “English” world might keep them out of heaven, so almost all of them return to become baptized. This is a fascinating glimpse at the little-known practices of a society that is as strict as it is remarkably open-minded and trusting of its young followers.

Tonight’s other highlights

Bob Barker hosts “The Price is Right” (7 p.m., CBS) before an audience of Coast Guard members.

Jeff Daniels stars in the 1990 thriller “Arachnophobia” (7 p.m., Fox).

“Live From Lincoln Center” (7 p.m., PBS) showcases eight new ballets written over the past decade.

Regis Philbin hosts an all-female round of contestants on “Who Wants to be a Millionaire” (98 p.m., ABC).

Scheduled on “Primetime” (9 p.m., ABC): new evidence makes a judge reconsider a life sentence.

Series notes

All are repeats … Ross deceives Mona on “Friends” (7 p.m., NBC) Drew Carey hosts back-to-back episodes of “Whose Line is it Anyway?” (7 p.m. and 7:30 p.m., ABC) Wrestling on “WWE Smackdown” (7 p.m., UPN) Improvisations on two consecutive episodes of “The Jamie Kennedy Experiment” (7 p.m., WBL).