The couple held hands as they walked up a pathway, the marble structure rising up in the haze behind them.
The prime minister marvelled at the site.
"It really is something, you have to see it to believe it," he said, then added "It's really a gift for all humanity."
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"My wife has tastes a little more modest and she also wants them while she's still living," Harper joked.
The prime minister is on a six-day tour of India that is heavily focused on trade but which will also touch on cultural links between the two countries.
Later in the afternoon, Harper was scheduled to participate in a business forum in the Indian capital of New Delhi.
Harper will also visit the technology and services hub of Bangalore, a buzzing city that symbolizes the kind of growth and entrepreneurship that Canada would like to tap into.
The prime minister's unusually long six-day trip to India will be heavily focused on encouraging trade and investment, but will also touch on personal ties between the two countries— namely, the one-million strong Indian diaspora in Canada.
Trade between Canada and India sits at a modest $5.2 billion annually, but the two countries would like that boosted to $15 billion by 2015.
Stewart Beck, Canada's high commissioner to India, said there are four main areas for potential trade growth: food security, educational services, oil and gas, and infrastructure support.
But major agreements are unlikely to be announced during Harper's trip. A foreign investment and a trade deal are both still in negotiations, and the two nations have yet to agree on the strings attached to Canada selling India uranium under a 2-year-old nuclear deal.
Part of the problem, Beck said, is that India is coping with its own internal issues. The country faces a controversy over how it has handled the taxation of British-owned Vodafone, and a scandal over the handing out of coal mining permits. The government of Manmohan Singh is also in a minority situation, and has not been able to move forward as quickly with economic reforms.
And Canada too has had his share of controversy in the area of foreign investment, with its recent temporary blocking of Malaysian company Petronas' bid for gas producer Progress Energy Resources, and its drawn out review of Chinese company CNOOC's takeover of energy firm Nexen Inc.
On the nuclear front, Canada has insisted on administrative conditions that would allow it to track exactly where the uranium sold to India ends up. India has balked at that.
India's economy is projected to grow by approximately 5.8 per cent in 2012-13, much lower than in previous years, but still healthy compared to that of some western nations.
CORRECTION: An earlier photo used to illustrate this story showed the Harpers outside Mughal emperor Humayun's tomb in New Delhi, India, incorrectly stating it was the Taj Mahal. The photo has been changed.