PAINTED HALL at the Old Royal Naval College

One of the greatest moments in cinema history comes when Dorothy steps out of her monochrome Kansas farmhouse into The Wizard Of Oz’s magical technicolour world. It’s a mesmerising transformation – and you can experience something almost as dramatic by heading to the Old Royal Naval College.

The last time I walked into Sir James Thornhill’s Painted Hall was at the end of 2016. Yes, it was an impressive sight but the combination of grime and time had made a nonsense of its boast to be Britain’s Sistine Chapel.

Soon afterwards the conservators moved in – and today, following an £8.5million clean-up of 4,000 square metres of baroque paint, this great artwork has been returned to its former glory, its luminous colours seeming almost to vibrate in the light of the hall’s state-of-the-art new LED system.

I freely admit I gasped when I saw the restoration for the first time. And I had to agree with ORNC chief executive Angela McConville when she told me there weren’t enough superlatives in the language to describe it properly.

The sheer scale of the revamp is awe-inspiring. Teams of conservators atop a vertiginous platform painstakingly cleaned the paint with little more than cotton buds in an operation watched by a total of 82,000 visitors.

At times it must have felt like the work would never end. But now that it’s finally over, the transformation is nothing short of miraculous and a tribute to the astonishing skill – and patience – of the craftspeople who performed that miracle.

There’s an added bonus, too. The entrance is via the newly-restored King William Undercroft whose lovely vaulted space now houses the hall’s ticket office, café and gift shop as well as some fascinating remains of the Tudor palace Placentia which once graced the site. ORNC conservation director Will Palin rightly describes the undercroft as a “beautiful prelude to the wonders above”.

Before this epic restoration project began, there was no entrance fee to the hall – instead, visitors were invited to put donations in a box. Now, however, people will pay £12 for a ticket, although anyone 16 and under goes free.

The new charge has faced anger in some quarters but the ORNC insist it has little choice because arts and heritage organisations across the UK all face government funding cuts.

A spokesperson pointed out that as well as entrance to the hall the ticket price includes a guided tour of the whole complex, daily talks, kids’ play items, a multimedia guide voiced by Game Of Thrones star Tara Fitzgerald and as many revisits as you like in the following year.

And from November 2020, on the first Sunday of every month all visitors will get in for just £5, with children of 16 and under going free. There will also be special discounts in the shop and café for residents of the royal borough.

For further information about visiting the hall and the rest of the historic site, go to www.ornc.org