North Asinara loop

This is a fantastic trail to run---gorgeous views, perfect solitude (in the off-season, but not recommended in high season (July/Sept) due to high temperatures and no shade at all), wild fauna (boars, wild donkeys, wild horses, muflons, pheasants, etc).

The first part, up to Punta della Scomunica is on wide service roads and very runnable. The descent toward Punta dello Scorno is more technical, some sections are steep downhill single-tracks, and with lots of loose rocks. If you go up to the Punta's lighthouse (I did, add about a half mile each way) it becomes even more difficult, especially on the downhill (coming back).

The return part (from the Punta dello Scorno back to Cala d'Oliva) is technically easier because the gradients are much more gentle. Expect old non maintained service roads strewn with rocks of all sizes. Runnable, but with care.

The return to Cala Reale can be run on a narrow coastal and almost non-runnable trail or on the main road (see below).

The views are breathtaking, especially from the top of Punta della Scomunica and near Cala d'Arena (which is in a max protection area and you can't go to). If you go off-season, you are likely not to find anyone---complete solitude: you, the boars, the donkeys, and the muflons (I ran into all of the above, plus wild horses near Cala Reale on my run back to the ferry from Cala d'Oliva).

It is not recommended in the summer, at least not as trail running. It gets very hot and the constant wind only makes it worse increasing dehydration. I did it in a sunny but cold day of May (53F, 20m/h wind) and went through 1.5L of water. I can't imagine running it in July or August with temps in the 80s and up. There is no vegetation higher than your knees on 95 percent of the trail . Moreover, there is absolutely no water to be found and you cannot get to the beaches in the protected areas (just in case you were tempted to cool yourself off with a quick swim).

More words of cautions:
- Cell phone service is spotty and unreliable (some providers are better than others, mine was non existent). If you are alone (I was) it may be a good idea to let someone at the Cala d'Oliva hostel (which is right where the trail starts) know your itinerary and your approximate return time. Just in case.
- Trail is technical--bring the usual first aid items
- Beware the trail is not marked. There are a few signs at the intersections, but no marks on the trail itself Not really an issue in the last part ( from Punta dello Scorno back to to Cala d'Oliva), but the first part crosses a few old unmarked service roads and old trails that may take you way off. Best to bring a GPS smart phone with a map app that works off line. Or map and compass.
-- Ironically, there is a marked trail (red and white stripes, the usual marks) on the very last section from Cala D'Oliva back to Cala Reale but it is interrupted by several closed gates along the way. I was able to open (and reclose, of course) a few, until I got to Trabuccato, where I find a fence running all the way into the sea and closed with a tied and locked gate. No way around it, I had to run up to the main road, go over the tall fence (no barbed wire, luckily, but still not easy), and run back on the cement road. The trail is very narrow and almost not runnable, anyways. You may be better off running on the main road from Cala d'Oliva to Cala Reale. Traffic is minimal, anyways, as tourist cars are not allowed on the Island.
And finally: the daily ferry rides from Porto Torres allow to do this run as a one day trip: Get on the boat from Porto Torres at 8:30, arrive at Cala Reale by 10. Run to Cala d'Oliva (5 miles/8km) or find a lift from the few local tourist operators, and yo can be back to the hostel by 3. Then do the same in reverse, and run back to Cala Reale or find a lift. Ferry takes off at 6pm and reaches Porto Torres at 7:20.
In mid and high season there are daily ferries. In low season (Oct to April included) you can do this only on Tu, FR, and Su .