Bulb gone in the chandelier above the stairwell. Obvious danger of falling onto the stairs and thence to Casualty or worse.
How do the bulbs come out? Pull, twist, unscrew, push in and turn? No idea? Access is, in any event, difficult.
A long and intrepid story cut short. The bulb pulls out and the new one pushes in. It's not smooth 'n' easy. You probably don't need to unscrew the surrounding shroud-thing first.