Been to enough biennials? Skulptur Projekte M nster only happens every 10 years. This, its fourth iteration (following 1977, 1987 and 1997), invites artists from all over the world--many of whom are returning to the city and the event--to create new site-specific works. Thus Michael Asher brings back his trailer and parks in sites he first sussed out in 1977, continuing to explore the conflicts between rigid form and mobile space, and to document the dramatic transformation of the urban environment over four decades. Guy Ben-Ner equips bicycles with screens and places them around the city; by pedaling, participants control the speed and direction of a film of the artist doing the same. Guillaume Bijl mocks up an archaeological site 25 feet square and 18 feet deep, whose steep walls imitate layers of soil. Visitors climb a grassy hill to peer into the pit from a balustrade; in the pit, a 14-foot, shingle-roofed spire topped by a weathercock preens. This extensive book inspired by and documenting the festival opens on 35 sections between 4 and 16 pages long, each designed by the artist and illuminating his or her work in text and images. Its second half comes in the form of a glossary of more than 100 key concepts linked to the subject of art in public spaces; artists, art historians, philosophers, urbanists, architects, sociologists and other writers weighing in with definitions from their respective disciplinary perspectives. Participants include Francis Alÿs, Isa Genzken, Mike Kelley, Rosemarie Trockel, Bruce Nauman, Martha Rosler and Pae White.