In many parts of the country, construction is a significant part of the underground economy.

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The site was originally intended to be a parking garage until construction uncovered a series of Roman ruins, now preserved in the underground Antiquarium museum.

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Declared the European Green Capital in 2010, Stockholm is investing in new construction like the City Line tunnel, which will put commuter rail lines underground and double the number of trains able to move through the city.

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It would involve the construction of a dam, reservoir, underground power station and water tunnels in the hills above Loch Lochy.

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They were all held in the same tiny underground cell with Roy Hallums, an American contractor working for a Saudi construction company who was kidnapped, perhaps with Al-Zubayi's involvement, in late 2004.

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This setback came a week after the announcement of further delays on one of Britain's largest construction projects, the extension of London Underground's Jubilee Line from Westminster to Stratford in east London.

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An example is engineering and construction group Balfour Beatty, one of the preferred bidders for London Underground PPP, which reported in August that PFIs underpinned its 17% rise in underlying profit growth.

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