Abstract: This paper presents a novel design of a Jiegged "spider" robot capable of moving in a wide range of two-dimensional tunnels. The spider moves in a quasistatic manner, by stably bracing itself against the tunnel walls and moving a free limb to a new position. The design has been strongly influenced by the recent immobilization theory of Rimon and Burdick [13, 15]. The theory dictates the minimum number of limbs such a spider can have, as well as the shape of the footpads. The class of tunnel geometries dictates other key parameters of the spider, such as limb dimensions and number of degrees of jieedom of each limb. We review the relevant components of the immobilization theoy, then describe the details of the spider design. The spider will initially move under a worst-case assumption of slippey tunnel walls, and we also descn"be a locomotion strategy under this assumption. The spider has been built and is currently undergoing locomotion experiments.