Lighting algorithms for outdoor scenes suffer from the sheer geometric and lighting complexity of such environments. In this paper we introduce an efficient, hierarchical solution to the problem of outdoor illumination. Data structures and sampling algorithms are presented, permitting the integration of complex and natural objects in a hierarchical radiosity simulation system. This new approach allows the hierarchical simulation of radiant energy exchanges in outdoor scenes for the first time, including terrain and botanical models as well as sunlight and skylight. This is accomplished by providing the necessary tools to treat terrain meshes as a hierarchy of light-exchanging objects, as well as an efficient hierarchical representation for the sky dome. In addition, refinement criteria are adapted to the particular characteristics of natural lighting. Results of our implementation are presented including naturally-lit images of terrain-maps, trees and buildings.