It was the largest architectural competition in history. The challenge? To design what would become the world’s biggest museum for a single civilisation.

Back in 2002, when the Egyptian government announced the call to create a home for its country’s archaeological treasures, more than 1,500 firms from 83 countries applied. Just over a year later, when the winner was announced, there was some astonishment that the Grand Egyptian Museum would be designed not by the likes of Frank Gehry or Zaha Hadid but by a small Irish firm: Heneghan Peng. “When we heard we had won,” Róisín Heneghan says, “we couldn’t believe it. We called them back and asked: Are you sure?”

Now, more than 20 years later, at a cost of more than $1 billion, the Grand Egyptian Musuem is finally set to fully open. The site has been opening in phases; at last, after a series of setbacks and delays, the entire complex will be on view from November 4th.

As this includes the entire Tutankhamen collection, previously shown only in parts, in the smaller and increasingly inadequate Egyptian Museum Cairo, on Tahrir Square, it promises to be extraordinary. Another star attraction is the Khufu ship, an intact solar barque originally sealed into the Great Pyramid more than 4,000 years ago.

So how did a Dublin architectural practice with a team of just 18 people triumph over some of the biggest and most famous architectural names? “The most important thing,” Shih-Fu Peng says, “is the site. There is the desert plateau. Egypt is defined by the Nile: it cuts through Egypt, and that’s where the civilisation was spawned. But the Nile would have no relevance without the desert plateau. The client had already chosen the site, so we could almost” – he pauses – “not screw it up.”

It is a reply typical of Peng, who combines intellectual heft with a strand of wry wit.

“Any practice that created an object,” he says, “irrespective of how you argued it – a [Frank] Gehry, a [Peter] Zumthor, a Herzog & de Meur