This great hall is normally kept private for members only but on Open House weekend...
Here's what Wiki says;
The Honourable Society of the Middle Temple, commonly known as Middle Temple, is one of the four Inns of Court exclusively entitled to call their members to the English Bar as barristers; the others being the Inner Temple, Gray's Inn and Lincoln's Inn. It is located in the wider Temple area of London, near the Royal Courts of Justice, and within the City of London.
In the 13th century, the Inns of Court originated as hostels and schools for student lawyers. The Middle Temple is the western part of "The Temple", the headquarters of the Knights Templar until they were dissolved in 1312; the awe-inspiring Temple Church still stands as a "peculiar" (extra-diocesan) church of the Inner and Middle Temples. There has never been an "Outer Temple", apart from a Victorian-era office block of that name: an order of 1337 mentions the "lane through the middle of the Court of the Temple", used by chancery justices and clerks on their way to Westminster, which became known as Middle Temple Lane and probably gave its name to the Inn. The Inns stopped being responsible for legal education in 1852, although they continue to provide training in areas such as advocacy and ethics for students, pupil barristers and newly-qualified barristers. Most of the Inn is occupied by barristers' offices, known as "chambers". One of the Middle Temple's main functions now is to provide education and support for new members to the profession. This is done through advocacy training, the provision of scholarships (£1 million in 2005), subsidised accommodation both in the Temple and in Clapham, and by providing events where junior members may meet their more senior colleagues for help and advice.
Middle Temple Hall is at the heart of the Inn, and the Inn's student barristers are required to attend a minimum of 12 qualifying sessions there. Qualifying sessions, formerly known as "dinners", combine collegiate and educational elements and will usually combine a dinner or reception with lectures, debates, mooting, or musical performances. Middle Temple Hall is also a popular venue for banqueting, weddings, receptions and parties. In recent years it has become a much-used film location - the cobbled streets, historic buildings and gas lighting give it a unique atmosphere. Shakespeare's Twelfth Night received its first recorded performance here, at the feast Candlemas in 1602.