One of the first major buildings to be constructed in the central business district in fifteen years is now rising toward the sky. The federal courthouse annex, at 19th and Champa streets, is meant to relieve crowding at the adjacent federal courthouse -- but it also serves as an impressive contribution to downtown. The new building responds well to the older one: Like the original federal courthouse, the annex has an elegant design -- although this one joins a finely detailed tower to a massive horizontal block. Conceived by resident modernist Ron Mason, a partner in the Denver firm of Anderson Mason Dale (with Hellmuth, Obata & Kassabaum serving as associate architects), the annex is destined to be among the city's best high-rises.