This motorless treadmill screams elegance - Sprintbok by NOHrD

The Sprintbok motorless treadmill is probably the best looking curved treadmill on the market. The slats and frame are made of wood and helps absorb shock and vibrations.

https://www.nohrd.com/gr/sprintbok/

There's also evidence that a curved treadmill burns more calories than motorized treadmill. Two studies: One shows that it burns 30% more and the other finds that it burns 44% more.

Studies on motorless treadmills:
Energy Expenditure During Sub-Maximal Running on a Non-Motorized Treadmill - March 2011The Journal of Strength and Conditioning Research
https://www.researchgate.net/publicat...

Comparing Calorie Expenditure and Rating of Perceived Exertion between the Curve and a Motorized Treadmill - 2014 Nicholas Robertson
Eastern Washington University
https://dc.ewu.edu/cgi/viewcontent.cg...