A few weeks ago, I got an email from a reader suggesting I check out the Woolworth Building. To be honest, I didn’t even know it was possible, thanks to the ‘No Tourists Beyond This Point’ sign outside.

But as I discovered, the Woolworth does open its doors to small groups – a new development over the past year – and as luck would have it, Adventure Club was organizing a trip there last weekend.

Adventure Club is a new idea by the Brooklyn Brainery. As well as teaching fun things in the classroom, they’re now helping New Yorkers see/do things in the city that they’ve never got around to. Earlier this year I helped Soma, one of the owners, come up with ideas for things to add to the club’s list (such as this one) so I was keen to see what else they had planned.

So on Saturday, I headed to the Woolworth, which is near the World Trade Center, to join the group.

As we stood in the ornate building’s shadow, our guide Bob explained that Frank Woolworth had been the tenacious mastermind behind the ‘five and dime’ stores, pioneering the practice of fixed prices, transforming shopping – and making his millions.

In 1913, he commissioned this neo-Gothic building in New York – splashing out $13.5 million and winning the title of the world’s (then) tallest building.

Yes, the outside is pretty – and includes interesting details, such as faces from Europe, Africa, Asia and America to show he was a man of the world – but it was the inside that really took my breath away.

The ceilings sparkled, the floors glistened and the guards looked very, very stern.

After being dazzled by the main entrance, Bob showed us around – pointing out details, as well as lots of ‘W’s to remind you just whose building you were in.

Then we went underground, where residents and workers once had access to the subway and where a vault still remains, in a nod to its history as a bank.

The building is now used by businesses, New York University and well-off residents. They’re also building a penthouse apartment, which can be yours for about $90 million.

But if you don’t fancy shelling out that sort of dollar, thankfully there are other ways to check out the inside. You can pretend to be a potential buyer, join some classes at the NYU School of Continuing and Professional Studies or see how long you can last before those stern-looking guards kick you out.

Or if you fancy getting a thorough look – which I really recommend – then keep an eye on tour dates on the calendar here.

(And if you’re looking for other cool stuff to see, why don’t you check out what Adventure Club has got lined up?)