The poem imagines a kind of travel guide for the inside of the mind, a book that would show us around "our own two heads." The title, "Head trip," plays on this: a trip is both a journey and, in slang, a mind-altering experience. The speaker treats the head like a place you could visit, with landscapes that are "fair and tunable," as if they were pleasant weather or a radio you could adjust, and with "people in them," the voices and memories we carry around.
The ending is a small surprise. The speaker admits these inner people "are not as I expected," yet finds them "pleasant to stone." That last phrase is odd and open. It might suggest being stoned, or something steady and solid like a stone, or a pleasure so strong it numbs. The mood is curious, light and gently playful. The speaker seems more amused and quietly delighted than worried by what turns up inside.