"It's the hardest thing I have ever done," says actor Patrick Stewart of the latest production of Samuel Beckett's Waiting For Godot, which is currently touring the UK.
Sir Ian McKellen and Patrick Stewart
The Royal Haymarket production features Stewart alongside stalwarts of the stage Sir Ian McKellen, Ronald Pickup and Simon Callow.
Speaking to Today presenter Jim Naughtie, the four describe both the creative pleasure and technical difficulty of performing Samuel Beckett's enigmatic characters.
"I don't think there will ever be a point where one can coast in this play. It is built in that your brain has to be functioning at 112%, all the time," says actor Simon Callow.
The drama is set around two central characters, Estragon and Vladimir, who spend two days waiting for the play's namesake.
The play caused shock waves when it had its London premiere in 1955 - a play without a traditional plot, two tramps pondering the meaning of life while they wait for a man who never comes.
But Beckett's language, his depiction of humanity at its rawest and most moving, has established Godot as a 20th Century masterpiece.
While Samuel Beckett never gave any hint as to the central character's background, Sir Ian McKellen has his own theory.
Ronald Pickup and Simon Callow
"They only meet each other in the evening. They are not married, they don't live together. Well who comes together in the evening? Performers do," he says.
"The idea that we might be coming to some ruined theatrical memory... it was very releasing for me."
Despite the sense of existential crisis that permeates the play, the performers are agreed on an underlying emotional depth.
"I struggle with my emotions every night, it is filled with such compassion," says Patrick Stewart.
And for Roland Pickup, despite the dark content, the overall effect on the audience is one of exhilaration.
"For the fact that it deals with bleak things, it is actually a celebration of the fun of coping with this crazy thing called life," he says.
This is an extended version of the broadcast discussion.