Compositionally, this is a very strong image. The lower camera perspective, and having the subject in the lower right works well for a balanced image.
Technically, there is blaringly wrong with this image. It is well-focused, your exposure is good, and the color tones are excellent.
Overall, it is a very good image. For the challenge, though, it is kind of weak on the "postcard" element. While I could see this being the type of card a tourist would buy if they were visiting this monument, for those that do not know what it is, or it's significance, it rather comes across as "I have a really good picture, so I will put it in this challenge."