The picture shows the main entrance to Conway Hall which is used till 10:30pm. After 10:30pm use the entrance in Theobald's Road.
Conway Hall, 25 Red Lion Square, London WC1R 4RL
Holborn station is closest. Russell Square and Chancery Lane stations are close enough.
Conway Hall's web site lists buses as follows:
Route 98 comes via Oxford Street and terminates in Red Lion Square. Routes 19, 38, 55 and 243 pass by the Theobalds Road entrance to the Hall. Any bus to Holborn, Grays Inn Road or Southampton Row/Kingsway comes close to Conway Hall.
Parking is free after 6:30pm in the surrounding streets.
Red Lion Square is awkward to navigate because it is one-way (clockwise) and you are not able to complete a circuit. Enter from Drake Street.