The lid consists of two trapezes (close to triangles) that form a rectangular shape together. Opening the lid is done by lifting one of the triangles.
GJS-500-7 also called GGG50 marks a strong and heat-resistant type of metal while GJS is a sign for Continuously Cast Spheroidal Graphite Iron - which describes a process in which the metal is continuously fed.
The lid is similar to another manhole cover made by the same manufacturer