If you want to create a custom linkage for your walker like the Klann variations shown in the video to the right, see customize.
Strider's linkage plans can be found here.
TrotBot's linkage plans can be found here.
Scott Anderson's 3D-printed TrotBot plans can be found here.
UPDATE: for improved functionality for Mindstorms Strider Ver 3, see these instructions for mounting the EV3 brick higher
The zig-zag surface of air filters can trip walkers, but they also provide small "steps" for climbing.