Think back across the two days. A fence becomes a storyteller’s stage; a confessed fib becomes a game instead of a sin. An old tree opens into a café with room for three. A picnic marches out under an explorer’s flag, survives one furious bull, loses and finds one small monkey, and comes home singing. Tommy and Annika’s summer — and their courage — will never be the same.

An oak can live for five hundred years or more, and the oldest oaks share a secret: many are hollow. A tree trunk has two kinds of wood. The outer rings are alive, carrying water and food between roots and leaves; the inner core — the heartwood — is old, dead wood that mainly gives the tree strength. Over long centuries, fungi can slowly digest this dead core while the living outer shell keeps growing. The result looks dramatic but is usually harmless: a healthy, growing tree wrapped around an empty room. Far from being a problem, a hollow oak is a busy address. Owls nest in the openings, bats roost in the dark, and rare beetles chew the soft, crumbling wood. Scientists say such ancient trees are among the richest habitats in northern Europe, and Sweden protects many of its oldest oaks by name. A child who finds a hollow tree has really found two things at once: a hiding place, and a little apartment house for wildlife.

No right or wrong — close the screen and tell someone nearby what happened in this part. Can’t find anyone? Tell yourself out loud. The moment you teach it, you truly understand it.