Some places and things you haven’t seen tend to seem bigger than they actually are. At least for me, the opposite could be said of the Sydney Opera House. I was surprised by how big it actually was, in large part due to some misunderstandings I had about what was inside its famous sails.

The Sydney Opera House is not, in fact, one large performance hall, but a combination of two main halls and a number of smaller ones. One of the large halls is indeed dedicated to operas. Though large, its mostly black interior – meant to place focus on the show up front and help project voices throughout the house – keep it from being very impressive internally.

The main concert hall, on the other hand, used by Sydney’s symphony and for countless world-class events in the past, is as magnificent on the inside as it is on the outside.

Rich wood panels are molded into angles that – from the perspective of the audience – make it tough to tell where the walls end and the ceiling begins.

As in every hall within the Sydney Opera House, seats are molded from a lighter birch wood native to Australia. Seats are staggered, row by row, so that no one’s view can be blocked by the person in front of them. Above the performers are a series of ethereal chandeliers, doughnut-shaped rings that act as natural amplifiers and monitors, allowing the orchestra to better hear itself.

There’s no set seating capacity for the main hall, as its stage can grow and shrink to accommodate a wide variety of events. Small ensembles and concert artists typically use less of stage, while full symphony performances and special events, require more area. Mohammed Ali once fought here even, so versatile is the hall.

Aside from these main halls, which jut out at slightly opposed angles from each other – leading to the staggered look of the “sails” that make up the famous outer structure of the building – there are a number of smaller venues within dedicated to ballet, theater and ensemble performances. Mel Gibson, Hugh Jackman, Nicole Kidman and others worked here before and after their rises to stardom. What’s most remarkable about these theaters, perhaps, is how unremarkable they are; nothing but location appears to separate them from the sort of basic theaters you’d see at the college or even high school level across the globe.

Of course, it’s the outside of the building that makes it famous. The design was first chosen as the winner of a competition in the 1950s, though the building wouldn’t open with a commencement by the Queen until the 1970s. What was once projected to cost less than $100 million, adjusted for inflation and in US dollars, ended up costing nearly a billion to finish. Paid for entirely through proceeds by a lottery program started in New South Wales to fund its construction, the Opera House was debt-free less than two years after it opened despite the massive cost overruns. Today, it’s one of just three buildings built in the 20th century listed as a UNESCO World Heritage site.

The sails might look like they’re a pure white from pictures, but closer inspection reveals a mixture of tiles both white and cream colored, millions of which together result in a very-slightly-off-white shade that reflects less heat back into the building and is brilliant-but-not-blinding to observers on a sunny day.

The giant sails are sometimes referred to as shells, but that’s not correct from an architectural sense. They’re more akin to ribs. Giant concrete molds were used to make these ribs one at a time to be hoisted into place, each building on the work of the one before to create the rounded effect.

The genius of this method is left bare for all to see on the inside. The architect’s style was extraordinarily minimalist on the interior of the building, outside of the lavish main concert hall, and you can see the marks and indents on the exposed concrete ribs where they were removed from their molds, hoisted by cranes and secured into place.

To see the Opera House only from the outside would be a mistake. The interior of the building shows how much more there is to the Opera House’s story than just its famous sails, and you can only see it by attending a performance or going on one of these tours. When in Sydney, make time and squirrel away $30 for one of the tours that run throughout the day. As a bonus, tour guests are offered a variety of discounts, both on dining options at the Opera House and on tickets for certain performances. You don’t have to be an architecture buff to appreciate Sydney’s greatest treasure.