(Reuters) - The 100th edition of the Giro d'Italia promises to be another mountainous affair as riders will need to climb the Stelvio pass twice during a grueling 16th stage in the third week, according to the course unveiled by organizers on Tuesday.

The 227-km stage, also featuring the ascent of the feared Mortirolo pass, will be held a day after the third rest day and two days before another 'tappone' (demanding stage) with five climbs scheduled for the 18th leg.

Climbing will start earlier, though, with the first mountaintop finish planned for the fourth stage which will end on the slopes of Mount Etna.

The 2017 race, which will start from Sardinia for the first time, will also pay tribute to former champions.

Stages will start or finish in the birth places of 1958 winner Ercole Baldini and five-times champion Fausto Coppi.

The three-week race will be decided with a 28-km final time trial from the Monza Formula One circuit to the Milan cathedral.

(Reporting by Julien Pretot, editing by Pritha Sarkar)