Since you've updated that you shot this with a 6D on a tripod, I can definitely say that I see what looks like a lot of ISO noise that was desperately covered up with way too much noise reduction. Really a lot - on both counts. I had actually originally thought this might have come from a compact camera the quality was so poor - it feels like the kind of in-camera processing a cheap compact does to try to hide the fact that it has a noisy, crummy sensor and a soft unsharp-y lens.
I would be very interested to know what ISO you shot this at - even in low light of the evening there should have been no reason to go much higher than ISO 400, even less if you had any sort of reasonably fast lens (...to go with that nice full-frame camera!). This looks like it was maybe shot at ISO-25600, then creamed to death with noise reduction. The whole image has an unnatural silky-smoothness that feels like the telltale of the noise-reduction slider pinned as far right as it will go.
As an aside, in addition to the chromatic aberration (noted by others), there is also some distortion from the lens (curving horizon, leaning verticals, etc). A professional shot would probably correct this, either in post with something like the lens profile correction in Lightroom or, even better, by shooting it with a tilt-shift lens in the first place.
The photo itself is otherwise great - maybe a bit oversaturated for my taste, but it's an image you should be proud of. IQ technicals can be hard to master.