When it comes to exhibition venues, the National Theatre may not spring instantly to mind. Yet it has lots going for it: the reliably engaging exhibition programme is free and the long opening hours are great if you're working (until 11pm Monday to Saturday). Theatregoers who arrive early for a performance are often rewarded with the serendipitous discovery of an engrossing display that's really worth a special trip. The latest, subtitled 'A Lifetime in Pictures: Robin Hanbury-Tenison', features photographs from the archive of the explorer, president of Survival International and longtime champion of the rights of tribal people. Also included are diary entries from his travels in Borneo, Burma, Brazil and the Sahara in the 1950s, 1960s and 1970s, along with artefacts that provide a glimpse of the threatened cultures that Hanbury-Tenison has championed for so many years.