The climb starts not too steeply up to Motel Spia, then the road steepens and encircles Monte Spia, then passes above the Cellina gorge. It's a mix of nice shady stretches and sun-exposed sections. It was nice and cool because I left before 0900 but by the time I reached end of pavement at 683 meters I was panting and drenched in sweat.
On the steepest bits I stood to climb, but managed to stay seated most of the time. The descent was fun, though I almost ran over a guy with a butterfly-net. Butterflies were everywhere (black or dark brown). Also a very large circling eagle.
The grade from Grizzo to the osservatorio: