The Outlander star is here to educate you on Scotland's quirkiest sights.

How about a wee Scottish history lesson courtesy of Sam Heughan and Graham McTavish?

In EW's exclusive clip from this Sunday's episode of Starz travel docuseries Men in Kilts, the former Outlander costars visit a familiar spot. Fans of the time-traveling, century-spanning series are used to standing stone circles. Indeed, they're pretty iconic on the show, with Claire (Caitriona Balfe) (accidentally, at first) time traveling by passing through them.

Sam Heughan and Graham McTavish on Men in Kilts.

On Men in Kilts, Heughan and McTavish visit the Callanish Stones on the Isle of Harris — the very ones the crew on Outlander made casts from to build the show's time traveling stones. But since the real life ones don't enable visitors to hop from century to century, what are they actually for? The guys are just as baffled as us. "Whatever reason they had for bringing things here, they had a reason," says McTavish in the clip, while Heughan runs through possible uses for them, including that they were used in a pagan ritual, or to mark a gathering spot, or to tell cycles of the moon, or — our personal favorite — "they may have been giants that were frozen." Hey, they've been there since 2900 B.C., so, truly, who can say.

Men in Kilts episode 4, titled "Witchcraft and Superstition," airs Sunday at 9 p.m. ET/PT on Starz.

Watch the clip above.

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