Liane Carroll, Sophie Bancroft & Sara Colman perform at the Grand Entrance Hall at Brunel Museum. The Grand Entrance Hall, where young Isambard Kingdom Brunel nearly drowned, was the world’s first underground theatre. Before the trains came, the chamber echoed with applause for acrobats, tightrope walkers and serenaders. It was also the entrance to the first undergound tunnel under the River Thames. First for pedestrians and eventually trains.