In geographical databases for navigation, users raise various types of queries concerning route guidance. The most fundamental query is a shortest-route query, but, as dynamical traffic information newly becomes available and the static geographical database of roads itself has grown up further, more flexible queries are required to realize a user-friendly interface meeting the current settings. One important query among them is a detour query which provides information about detours, say listing several candidates for useful detours. This paper first reviews algorithms for the shortest and k shortest paths, and discusses their extensions to detour queries. Algorithms for finding a realistic detour are given. The efficiency and property of the algorithms are examined through experiments on an actual road network.