A walker includes a frame with downwardly extending front and rear legs. An obstacle traversing wheel assembly is disposed at the lower end of each front leg, and a wheel having a brake that is engaged by a downward force on the walker frame is disposed at the lower end of each rear leg. The obstacle traversing wheel assembly is arranged with a primary wheel that is rotatable about a central axis. At least four secondary wheels of equal diameter, but smaller than the primary wheel, are arranged at fixed locations around the circumference of the primary wheel. The secondary wheels are arranged to freely rotate independently of each other and of the primary wheel.