The speaker hands out advice that sounds like a remedy: if you fear losing your sense of wonder, visit the beach, the library, the gardens, the aquarium. The first few suggestions are grand and a little excited, with "infinity" and "magnificent variety." But the list slowly sinks. Staring at palm trees and seeing the fish feel more modest, and then come work, which is "infinite" in its toil, and finally a cemetery full of old tombstones. Wonder, the poem hints, can be found in pleasant places and in dull or sad ones too.
The ending changes the tone. The speaker turns to "you" and says, "You can't fool me," insisting the listener never lost wonder at all. The speaker admits that they may have lost it themselves and regained it from this person. The mood is playful and dry at first, with a gently comic list, and then becomes warm and sincere. The advice was never really about places. It was about being around someone who still notices things.