Obstacles are but pleasing for many aspects of large realworld sensor networks. Among other things, the presence of obstacles distort the sensor node localization process and might lead to costly routing because of unnecessary detours and/or dead ends. In order to relieve these problems, this paper proposes a distributed obstacle localization algorithm, called DOL for short, in which the sensor nodes interact with each other mostly locally. The proposed algorithm is very resource and communication efficient in that all sensor nodes send only a small number of additional messages. Finally, the sensor network fine tunes the employed routing algorithm. Categories and Subject Descriptors C.2.4 [Distributed Systems]: Distributed applications General Terms Algorithms, Design, Theory Keywords obstacle localization, local interaction rules, wireless sensor networks, routing, multi-hopping