I am a colorful kingdom beneath the sea, built by tiny animals yet larger than many cities. What am I?

What stretches like a spine across an entire continent, yet has neither life nor limbs? Solve the riddle → What was once criticized as an ugly construction, but is now an iron monument that breathes with the seasons? Solve the riddle → Its short borders enclose art treasures and an undeniable spiritual leader, in the heart of an eternal city. Solve the riddle → What flows upstream in history but always runs north, through the heart of the desert? Solve the riddle → Which railway spans seven time zones and is so long that you can eat breakfast in Europe and dinner in Asia during the same journey? Solve the riddle →