Double ascent. Turó de Sant Elies, Pla de la Calma.

Two Peaks back to back, with more than 2000 meters of accumulated ascent.
Almost the whole trip is by wide dirt track, except a couple of short sections of single track, and the last few km, which descend from Montseny to Sant Esteve by asphalt road. The trails on the first ascent are all in excellent conditions. People live in this area, and you might meet cars.
The first 50-100m of descent after Sant Elies is a "non-trail" where you have to navigate rocks and roots in between trees, while descending a steep incline. The crazy ones will lower their saddle, and enjoy navigating the "Cool Features", while the faint of heart might want to get off the bike and walk down while avoiding the "Nasty Obstacles".
After that it's back to the wide track for the rest of the first descent, first out in the open, and then slightly narrower tracks in the forest.
Make sure you stop at the fountain to fill up on water, as there's still a long way to go. And beware of hikers. The forest in this area seems to be quite popular, and I had to slow down a few times to pass groups of people.
The second ascent is by dirt trail also, first along a stream through the forest, and then in the open, climbing up the side of the mountain with awesome views throughout. The track on the second ascent is rougher than on the first, with more rocks and loose stones, and in some places large rocks have fallen on the track, making access by car impossible.
When you get to the top the landscape changes completely. This is the Pla de la Calma, which is all meadows and green pastures for sheep and goats. The trail, which weaves through the hilly landscape for a few km, is still quite rough in places, with rocks peaking through and muddy patches.
The descent from Pla de la Calma transitions back into the woody landscape from before, and the trail is in good shape for most of it. Lot's of fun bits with plenty of opportunities for building up speed. However, make sure you slow down when you pass through one of the small communities that live here. You are likely to see people, kids, cats etc, lounging about on the trail. So be safe, and slow down when you see a house up ahead.
Before reaching the town of Montseny, the dirt track ends, and you're stuck with the asphalt road for the rest of the descent. Boring but comfortable.