It's a pity to run this far in the Sintra area and not pass closer to Cabo da Roca and a couple of other well-used trails/attractions nearer to Sintra town. The route's pretty pattern makes me suspect it was once a race course. These days, quite a few miles of the route aren't well-used / maintained, or have been replaced with nearby/adjacent dirt tracks. I'd also stress that the route felt very "same same" -- if you're thinking of trail running here, you can see just as much in a route of half the distance.
Backtracked many times - Garmin can be a bit slow and imprecise in Sintra area, from prior experience. There are a lot of trails close together so it's easy to veer off for a few moments and have to come back. At approx. mile 20, the route cuts off the dirt track into the woods to avoid 3 separate Restricted Area locked gates.. was unconvinced it's not still private property, so i wasted a huge amount of time (~20mins) wandering around to see if there was an alternate/better path. Spoiler: there isn't 😅🤣.. so i continued, though by this point just wanted to be done with it and the "jogwalking" started in earnest.
Future attempts:
I'd kept a relaxed pace up to the 18 mile mark -- of my 4h56 time, approx. 25 mins were purely wasted/off-track, and an additional 20+ mins were me slowing down due to apathy in the last 9-10 miles. The route can certainly be completed in 4h10 or less.
Specific to today:
Weather was 18C/64F (in late December), very humid. There was rain earlier in the week, which made normally loose sand a bit easier to traverse, but created some fun little "sand sinkholes" that almost felled me a couple of times. There were puddles and mud in many places, and at the higher points of the route, it was raining and very windy. Peninha had near-whiteout conditions, which is a real bummer as that view would have been the highlight of the route. TBH any route pictures today would have been depressing rather than inspiring. An upside of the weather was far fewer walkers and mountain bikers than would be expected during the holiday season.
Food/water - Unsupported. Brought 3 gels and 1150ml fluids and went through it all. wish i'd had more calories given the extra time backtracking :-) there might be a public tap or two near enough to the trail (esp. when passing through towns), though i didn't specifically see one.