The AT-AT walkers are slowly advancing on Echo Base in Martin Harris' Battle of Hoth diorama. It's a huge one that includes everything we've seen in The Empire Strikes Back: Snowspeeders, a complete rebel base, a giant snowy battlefield and a some other tiny things.
Here's a video from The Brick Show showing all of this at the 2015 Brickfair:
Here's some hungry rebels:
A baby AT-AT:
And Darth Vader on a sleigh: