The 10178 Motorized Walking AT-AT was a set released in 2007.
The set can actually walk, and it is run on batteries. It consists of 4 minifigures Luke Skywalker, General Veers, AT-AT Pilot and 1 Snowtrooper. The middle has a handle inside the top for easy carry. It consits of over 1,000 pieces and includes a power functions battery box and motor to make it walk. Although it has the ability to walk there is no room to store minifigures or gear. This set is Exclusive and can only be purchased directly from the Lego® Catalog or on its online web site. It costs 129.99 American Dollars, and due to its popularity it is always on back order.
The armor plating on either side can be opened to access the controls to make the AT-AT walk forwards or backwards. It can also move up and down, and side to side. The cockpit door can be opened to seat the AT-AT Pilot and General Veers at the controls.
LEGO.com description[]
This is an official description which was taken from LEGO.com. Please do not modify it.
Behold the power of the Empire! For the first time ever, the ultimate Motorized Walking AT-AT is ready to crush the Rebel Alliance at your command. Thanks to the new Power Functions System, the mighty All-Terrain Armored Transport really walks forwards and backwards into battle! Features opening cockpit and rotating laser canons and stands over 12" tall and over 14" long. Includes AT-AT Pilot, General Veers, Snowtrooper, and Luke Skywalker with Grappling line and lightsaber. Requires 6 AA (1.5v) batteries, not included.