We're always talking about gateways, but I for one have no clue what they look like.
I recommend searching for "ground station" instead of "gateway" if you want to see images. Think of a virtually empty lot of land with a building and ginormous reflector(s). They're extremely secure, though. Couldn't even get an appointment to take a short tour of one of ours, but I don't think I missed much as they look a tad...well...boring.
I've been picturing it as similar to a cell tower site, with the small building and a large dish (or more) instead of the cell tower.
Here's a page on Echostar's ground station in Gilbert AZ. Not sure how accurate or current it is.