Spies Travel, which is part of the Thomas Cook Group , is offering discounts for Danish mothers to send their grown-up children on an activity holiday, in hopes it will hasten the arrival of much-wanted grandchildren.

A Danish travel company has launched a unusual campaign to heighten clients' sex drives and ultimately boost Denmark's low birth rate.

The "Do It for Mom" campaign asks for a "donation" of at least 25 Danish krone ($3.74) towards a holiday package, which Spies will match with a discount of up to 1,000 Danish krone ($149).

Denmark has one of the lowest birth rates across Europe at 1.7 children per woman, according to 2013 World Bank data. That's already down from 1.9 back in 2010.

"It puts our welfare and Spies' future business under pressure," a translation of the campaign landing webpage explains. "But those who suffer most are mothers who may never experience [having] a grandchild".

The accompanying video ad gets a little racy, but include shots of a sad grey-haired woman sitting alone in the park or flipping through photo albums in an empty home.

"Send your child on an active holiday and get a grandchild within nine months," the video promises.

But all good wishes for population growth aside, Spies' Head of Marketing Eva Lundgren admits it's a creative ad gimmick that's mean to promote the firm's "active" travel packages