"The Tollund Man" begins in the speaker's imagination. "Some day," the speaker thinks, he'd like to visit "Aarhus," the city in Denmark where the Tollund Man himself was discovered in 1950.
This is an allusion to a famous bog body (that is, one of several Iron Age mummies discovered in peat bogs). The Tollund Man is one of the best-preserved of all of these bodies; though he's 2,400 years old, visitors to the museum where he rests can still see the stubble on his chin—and the noose around his neck. Many researchers believe that he was strangled as part of a religious ritual, a human sacrifice to appease nature gods.
But at the outset of the poem, the speaker isn't focused so much on the Tollund Man's grim fate. Instead, he's looking at his calm, gentle face. The mummy's skin is stained "peat-brown," and his closed eyelids make the speaker think of "mild pods," a metaphor that suggests the Tollund Man looks a lot like the old, rich, partly-decayed vegetation of the peat bog he was found in. It's as if he himself has become a kind of earth god.
But if he looks strange and earthy, he also looks very human. He's wearing a "pointed skin cap"—an everyday detail that reminds readers both of his humanity and his great age. (One doesn't see too many pointed skin caps on the street these days.) And those seed-pod eyes are "mild" and gentle, as if he were peacefully sleeping.
The speaker's careful imagery in this first stanza suggests that he's already spent quite a bit of time looking at the Tollund Man. Remember, he's only imagining a visit to Aarhus here; all his previous acquaintance with the Tollund Man must have been through photographs. He seems to have developed a fascination with this astonishing mummy from afar. And his interest isn't purely archaeological: even his dream of visiting the Tollund Man already sounds rather like a religious pilgrimage.
This poem will trace the speaker's reflections on Tollund Man—reflections that will travel from the Iron Age right up to 20th-century Ireland, where, in the speaker's unhappy opinion, some version of human sacrifice is still going on.