This image isn't as good a composition as I would like but I was entranced by the Green Door. In doing some research I found the following:
One of the most amazing things about the Temple of Romulus is the door. This is not just a green door, or even a green bronze door. This door dates from the late Imperial Age and is therefore almost 1,700 years old. To have survived intact for so long and through so much is almost unprecedented. This is one special door.
But enough about the door, what about the rest of the building? It is situated in the Roman Forum next to the Temple of Antonius and Faustina, and dates from the early 4C. Originally it was thought that this was dedicated to Emperor Romulus who died in 307. Recently it has also been suggested that the building may have been associated with the Temple of Jupiter or the audience hall of a city prefect.
Maxentius bagan building the Temple of Romulus, and it was completed by Constantine. That is in such good condition is thanks in part to the fact that in the Middle Ages it was incorporated into the atrium of the church of St. Cosma and St. Damiano. Inside the church is a 6C mosaic showing Jesus Christ surrounded by several saints at his second coming. The rest of the church has taken over the Forum Pacis built by Emperor Nerva.
Although not a great image, I hope you can enjoy the history and siginificance of the Green Door.