Wicked, i am so glad you made the summit of Llewellyn.
I can see where you went wrong at the Eigiau carpark.
The route you took is part of the famous Welsh 1000m Peak Race, where runners and walkers start at Abergwyngregyn on the coast, make for the summit of Llewelyn, and Carnedd Dafydd, and then heading back along the Carneddau ridge, and joining the route you used to the summit of llewelyn.
When you entered the car park in Eigiau, there was a style on your immediate right,in the corner, just opposite the massive pothole, deep enough to damage most cars.
You should have used this path, and then followed it for around a mile, before reaching another style, and then bearing up Left, and joining the route that leads up the mountainside.
Ive never seen a big riggly snake, let alone a venomous one, are you sure it was an adder, not something far more dangerous.
Its ever so easy, when your familiar with the route, but i can certainly understand why you went wrong, as there are no waymarks or pointers.
You could not have had better weather for this magnificent walk, and you can probably now understand why i was so concerned about advising on the best weather conditions.
Route finding is pretty challenging, when you are unsure of your direction, and when the mist comes down above 3400ft, its anyones guess where you will end up, as i learnt to my cost some years ago.
I spent the best part of over an hour, going round in circles on Llewelyn's summit, totally lost, aiming for the summit of Foel Grach, but having to make for Ogwen.
My car was back at Eigiau, and i had to phone a friend for a rescue mission, of collecting me at Ogwen for a lift back to Eigiau.
He saw the funny side of it,but not everyone would.
So glad you saw Llewelyn in the best possible weather.