Narnia provides a nice option to hike a short trail through the woods while at the beach. It is open for all trail purposes, so watch for bikes and horses. The trail is well maintained and easy to navigate.
The trailhead (sign has "1") is about a quarter of a mile north of Seabrook along SR 109. From the trailhead, the first tenth of a mile is through a lovely tunnel of trees, which is a nice start to the hike. It then dumps out onto a service road, which leads east into a heavily logged area. The trail is well signed: continue straight after a quarter mile along the service road, then turn right after another third of a mile. The trail then returns under cover of the trees, still mostly a broad, flat service road. It's a second-growth forest, with sparse undergrowth and lots of thin, straight trees.
Two tenths of a mile into the woods, there's an intersection with another trail from the west. Continue straight (south) on the Narnia trail. After a third of a mile, come to another intersection with a trail heading east. There's a Narnia sign here ("2") for the north/south trail.
The final third of a mile brings you to the other trailhead ("3") in the Seabrook South Farm area, just down a path from the Orchard. Walk the streets a half-mile back to the town center.