In the lobby of an up-market hotel in a Copenhagen suburb, a suit-clad businessman pedalled away on a stationary bike, periodically glancing at the counter to see how far he had gone and how much energy he had produced.
"A bit more sweat and I'll have pedalled enough for a free meal!" said Ruediger Spaetel with a smile as he changed gears.
On a business trip from Munich, Spaetel is staying at the Copenhagen Crowne Plaza hotel where guests are asked to help produce the building's electricity by climbing onto stationary bikes.
The energy produced by pedalling guests is stocked in a battery before being injected into the hotel's power supply.
Spaetel, in his 30s, says curiosity led him to mount one of the two bikes parked in the hotel lobby after checking in.
"This allows us to help reduce our carbon footprint in a healthy way," he told AFP, adding that he was thrilled by the concept.
Adding to his enthusiasm is the fact that the hotel, which brands itself as "100 per cent green", has put a price on its guests' sweat: producing 10 watt-hours of electricity, generally achieved with an eight to 12 minute workout, will earn the German businessman a Euro 27 voucher at the hotel restaurant.
The hotel's communication director Frederikke Toemmergaard estimates the establishment has offered a free lunch or dinner to more than 200 eco-conscious guests since the one-year experiment began in April.
The hotel itself opened last November, just in time for the UN Climate summit hosted in the Danish capital.
Built not very far from the Oeresund strait that separates Denmark from Sweden, the Crowne Plaza's concrete and steel tower is covered in some 1,500 solar panels that produce 170,000 kilowatt-hours of electricity, which is enough to power 55 households.
In the basement of the 86-meter skyscraper there is a geothermal well which covers the hotel's heating and air conditioning needs, slashing its energy bill by about 90 per cent.
And in each of the 366 rooms, personal care accessories are biodegradable, taps are equipped with water-saving devices and all light bulbs are low-energy.