The poem begins with a remark about snakes: someone points out that half a dozen of them, from three species, had been hiding in the walls during a bathroom renovation. The speaker isn't much bothered by that. What sticks in his mind is something stranger and more dangerous, a huge nest of razor blades hidden behind where the mirror had been. It's a funny, slightly eerie detail, and the poem never explains it.
Then the scene opens out. With the walls gone and the roof propped up, the shower stands exposed to breeze and rain for half a summer. The speaker clearly relishes this. His closing sigh, "Ah," leads to a cheerful, almost grand declaration that he'll never have a better bathroom, no matter what else life brings. The mood is relaxed and wry, with a touch of wonder. Danger and discomfort are there, but the speaker treats them lightly and finds real pleasure in showering half outdoors.