based on size and construction maybe a chimney cleanout door....I'm certain there are lots of obsolete parts and fixtures that were once a part of boilers and coal stoves constructed in the last century and a half that are no longer used or recognized these days since we have moved to more efficient and cleaner ways to heat our homes etc
It looks like it is to hung by the holes and the two extending part suggests for something to hang from the square hole makes think with the old cook stoves where a square handle was used to left the round plates as the stove top plates.its decorated being one makes me think something for ladies but what may be to hang fire place gear up. Maybe someone at one of those old hardware fellows could say.