Everything to scale means big things are big
DeviantArt member Andrew McGee has visualized each of the various Colossi from Shadow of the Colossus into one image, showing exactly how they compare to one another in scale. It's a breathtaking image, especially when you consider how large your own character is in comparison, let alone how big these dang things would be in real life. Man, that underground still gives me creep-crawly nightmares.
Epic does not begin to describe the scope of all of them together, but if you'd so chose, you can adorn your wall with a poster size print from here, or just check out the hi-res version from Andrew's DeviantArt page.