What was your brief for the Giant's Causeway Visitor Centre?
The National Trust wanted a 1,800sq m replacement visitor centre plus car parking for 400 cars. We had to demolish the existing visitor centre, provide a temporary spot and then redistribute all the roads around the site, while we were building the new centre. Because we were building on a World Heritage Site, the new centre had to be more or less the area of the original building.

What was your starting point for the design?
The car park was intrusive for the site, but it was essential because the only real way of getting to the Giant's Causeway is by car, and there were problems with people parking on the very narrow local approach roads.

We didn't want to create a building that was surrounded by car parking, so we decided to integrate the parking with the building. The other consideration was the fact that people clearly don't come to the area to see a visitor centre, they come to see the Giant's Causeway site; we want them to be first of all aware of the landscape.

We cut into the earth to create two folds in the landscape – one accommodates the building, and the other hides the car park from view. Between the folds is a walkway that leads to the coastal ridgeline.

Can you describe the design of the visitor centre?
The structure is concrete, and so it’s quite a heavyweight building. It's built into the earth, so we continued the grass over the top of the building, but because it's a World Heritage Site we had to be quite careful with the seeding of the grass; we needed to use seeds that were collected locally. There was a fairly extensive trialing period that went on for two years, where seeds were collected from the National Trust, then we trialed them with more durable seeds, because people were walking on them, and eventually we found one that worked for the roof.

We used basalt stone for the façade, from the same lava flow that formed the Giant's Causeway columns.

If you are walking along the coastal path, which continues for miles, you just come upon the visitor centre. You can walk over the roof, look down through the skylights into the exhibition space, then walk into the building.

What is the internal space like?
We were constrained by the fact that we were building on a World Heritage Site, so the centre is not very big, considering the number of people that come into it on peak days. Because of this, we designed it so that it was very simple to navigate.

When you come into the centre, what you see is a straight line through the building, with light at the end. To your left there's a payment desk and a café, then further on there is a retail space and an exhibition area. To your right is a toilet. If you just walk straight through, you walk out and down to the stones. It's a very simple space.

How did you achieve the BREEAM Excellent rating for sustainability?
The building has ground source cooling and heating – the cooling was a bigger issue, because of the number of people in the building, and also because the exhibition has lots of electronics and computers. The skylights bring in a lot of daylight, even though the building is sunk into the earth.

Water conservation and management features have been employed, and we tried to source the materials locally as much as we could.

What were the biggest challenges of the project?
Getting the parking right was a big challenge. We needed to put a lot of parking into a very constrained site and we had to be careful not to overwhelm the site visually. It was difficult getting the flows to work to avoid people and buses crossing over, and it was tricky even from a planning point of view, convincing the road engineers that ours was a sensible solution.

We had to think about things like not letting the car park get so crowded that coaches couldn't turn around. It was very pedestrian, ordinary stuff, but was definitely the most complicated thing about the project.

What is your favourite part of the design?
Going up onto the roof. When you're up there, you can see down onto the cliff, and you can look back at the landscape, back to [the village of] Bushmills – it's something you couldn't have seen before.

If you're walking along the coastal path, it's kind of a surprise; people don't realise there's a building here. They start to notice things, like the fact that the paving and the handrails start to change, so they realise something is happening, and then they realise there's a building under them.

What's been the reaction to the building?
The National Trust is very happy with it. We put in a lot of work with the Trust and their operational people during the design phase to get the building to work for them, and I think that really paid off.

What drew you to a career in architecture?
I have no idea! I think I was about 12 or 13 when I decided I wanted to be an architect, but I don't know why.

I studied architecture at University College in Dublin, and Harvard in the US. In between, I worked at a variety of offices in New York.

I met [Heneghan Peng co-founder] Shih-Fu Peng at Harvard. When I left Harvard, I was working for Michael Graves in New York, and at the same time Shih-Fu and I were doing ideas competitions together. We won the first one we did, then nothing happened for years, then we won another ideas competition for a football stadium in LA in 1999. In the same year we were selected for the Architectural League of New York's New Architects programme. After that we decided to do real building competitions. We won the bid for a civic office outside of Dublin in 2001, and relocated to Dublin.

We won the competition to design the Grand Egyptian Museum in 2003 [the competition attracted 1,557 designs from 83 countries]. That was our first really big win as a practice, and it was a great feeling.

Who do you admire in architecture?
Rem Koolhaas, more for his thought processes than his actual buildings.

What do you enjoy most about your job?
Probably the beginning of the design process, because things are much more open at that point.

Can you describe your vision for the Grand Egyptian Museum?
The site is very close to the Giza Pyramids – about 2kms away. It's going to house the collection from the current Egyptian Museum.

The site itself has got a significant difference in levels across it – about 50m – created as the Nile carves its way through the desert. We have created a new 'edge' to the plateau with the museum's façade wall. We thought that it would be nice if it was translucent, so that it comes alive when it gets dark – the façade is created from translucent stone that transforms from day to night.

We also really wanted people to see the pyramids when they were inside the museum. We thought that from certain places, the pyramids should almost be visible in one view, so that you can see the extent of the collection. That's what really drove the design, because that had a whole series of knock on consequences.

The museum is currently under construction, and is due to open in 2015.

Tell us about the Palestinian Museum you designed near Ramallah in the West Bank
The 2,500sq m museum will explore different aspects of Palestinian history and culture. It’s being designed as a hub, because it's so difficult to get into Palestine, so there will be other museums in other areas which are more easily accessible. This museum will be the generator of a lot of the content for the other museums. It won't have a permanent collection, it will have exhibition space with temporary exhibitions. It will house quite a lot of administrative functions, as well as support spaces, a café and the gardens, which will be part of the museum.

The first phase is due to open next year. If it's successful, a further 5,000sq m of museum space could open in a second phase.

Where did the vision come from?
It's based on the idea of Palestinian agricultural terraces. The museum itself is not very large, but the terraced site has a series of gardens, and these will be part of the museum.

We talked to the landscape designer about the fact that you could tell the story of Palestine through the gardens. The area has been a crossroads for so many people, and the plants tell the story about the occupation of that landscape.

If you take the orange, for example, it came from Asia. So you could look at the trade route from Asia, you could also look at menus, food and dishes which have been built around the orange. That could be one way of telling the story of Palestine without getting too caught up in the politics.