Theatreland Tour with Ian McKellen
Out to the terrace
Here there's a terrace overlooking the Thames just through the building straight ahead. Go on through the central door. There’s a sign above the door that says “Seaman’s Hall”. That’s the door you want. Go straight through and out the other side.
Don’t worry, it’s perfectly alright for you to go through.
And if anyone does stop you, simply tell them you have the disembodied voice of Ian McKellen muttering orders in your ear and that you shall pass. They should leave you well alone after that.