The cover is dedicated to the renowned Japanese composer Yuji Koseki and his well-known song "The Highland Train Goes On".
It is part of a series of covers designed by students of a special needs school in Fukushima, inspired by the composer’s works. Koseki was born in the city.
The Fukushima City website identifies this as a 汚水ます蓋 (Ousuimasu-buta), a cover for a small wastewater access chamber. Accordingly, the cover has been classified under the sewage category.
Another cover dedicated to a different song by Koseki is also featured on the site: