A venture down the Ob River and into the heart of Siberia by Wall Street Journal Berlin bureau chief Kempe, who offers telling vignettes of a region now in flux but once as notorious for its climate as for its infamous history. Over five weeks in the summer of 1991, Kempe was part of a Russian-European expedition--which included Greenpeace scientists monitoring environmental damage as well as a member of the Supreme Soviet--that followed the course of the Ob, which rises near Mongolia and then flows north to its mouth, beyond the Arctic Circle. Though the expedition used a specially chartered boat, Kempe and his companions also made side trips by helicopter and train to visit local landmarks. The journey began in Kemerova, heart of the Siberian coal-mining and industrial region; continued on to Kolpashevo, grisly riverbank site of one of Stalinism's mass graves; and ended with a journey by train to Vorkhuta, once a notorious gulag in a region home to most of Russia's nuclear program. Kempe was the first American allowed into Tomsk 7, a planned town run entirely by the defense ministry; he also visited oil-drilling sites and spoke with native reindeer-herders. Everywhere, he and the accompanying scientists heard alarming stories of environmental damage and saw examples for themselves. In most places, local water is so contaminated as to be undrinkable, and widespread destruction of the fragile tundra threatens to become more significant than that of the rain forests. Along the way, Kempe talked to a variety of people, including a former prisoner who claimed to have tried to assassinate Stalin, and the son of a native people's shaman. Despite intermittent observations on the Siberian tendency to hold fate responsible for everything, more an anecdotal than analytical account of a place ``that has always been more a warning than a region.'' Timely.