Quarries often have great views being dug into and out of the sides of hills. But even with that the Trefor granite quarry cut into the side of Garn Fôr aka Mynydd y Gwaith [mountain of ‘the works’], one of the 3 peaks of Y Eifl on Pen Llŷn, has extraordinary views!  The main view, north-east, with Gyrn Goch , also igneous and also quarried, on the right, and over the sea toward Dinas Dinlle and Caernarfon on the left, is simply stunning! AND the view of the quarry itself is equally though differently awesome as the early 20thC concrete buildings rise up like a vast castle on the hillside! And it’s said that on a clear day both Ireland and the Lake District can be seen from the highest peak! 
The technicals; “Yr Eifl is an igneous intrusion and the resulting stone is a ” fine to medium grey granite (microgranodiorite)”  It’s a very hard granite and so was much used for road setts and is “an impressive 440 million years old”!  There are a number of different types/colours. “In the geological literature the Trefor Granite is referred to as The Garnfor Multiple Intrusions. This indicates that it is composed of several different types of granitoid rock, three types can be identified in the quarry. These are referred to by the quarrymen as pink, blue and grey granite, all of which are used for curling stones”  I spotted 2 obvious different types, a blue-grey and a pinkish. See photo.
The quarry is variously known as Chwarel Trefor / Trefor Quarry or Chwarel Yr Eifl / Yr Eifl Quarry for the mountain it is cut from. It is said the name Trefor/Trevor was that of the first quarry supervisor a Trevor Jones. The village was also named after Mr Jones too!  Some references call it Trevor Quarry and it’s possible that when founded the Anglicised name was used but since the 1970s the village is now called by the Welsh version of Trefor. [It sounds the same btw! :-D] 
The quarry opened in 1830 or 1850, [conflicting references] with a pier connected by an incline railway being built by 1870. This was horse-worked till steam locomotives were introduced in 1873.  A short branch line served the village of Trevor at the foot of the incline but this was closed before 1920. The massive concrete structure appears to have been built in the 1920s. From 1951 onwards the railway was gradually replaced by road transport. The main incline was abandoned in 1959 and the railway finally closed in 1962.  
The quarry is still operated on a very small scale for curling stones but is mainly abandoned. Note in the photo the circles where ‘cheeses’ have been cut out of the rock for the curling stones and the different colours .  
I don’t have a strict link connection of Trefor with London but for a quarry that “developed to be the world’s biggest granite quarry, and by 1931 had produced 1,157,000 tons of setts.”  it seems very unlikey that none ended up in London and are not still under our feet or wheels on our London roads, even if buried beneath layers of tarmac and asphalt. And, follow me here, there are also references to Penmaenmawr setts being used in London and as ‘The Welsh Granite Co. Ltd’, who owned Trefor, merged with the Penmaenmawr and Llanfairfechan quarries on the north coast to form the ‘Penmaenmawr and Welsh Granite Co. Ltd’ in 1911 … it’s also possible that Trefor setts were labelled Penmaemawr setts. And lastly. Most evidence shows Penmawenmawr granite heading to Lancashire by boat,  but Trefor is closer to London by a good few miles so maybe that would have influenced decisions. A study of the newspaper archive would show more clearly but that’s for another time!
I try to keep as much of the contemporary media my own but this drone footage from DMC Production is great! https://www.youtube.com/watch?v=BehD-Z6XgkM by DMC Productions
And some more photos.
There’s lots to see and there are public footpaths going right up to the main buildings.
The harbour is open for all and I would have liked time to wander around the village.
At the back of Garn Fôr there is another smaller quarry and incline and the ex-quarry village of Nant Gwrtheryn, now a Welsh language centre but I’ll do a post on that at some time.
– Public Transport
Chwarel Trefor/Trefor Quarry is a long way / takes a long time to get to from London. Pwllheli and Cricieth, which are 8 or 9 walking / cycling miles away from Trefor, are actually on the railway, but it’s a 5 1/2 hour stopping rail service from Birmingham, so 8 hours from London. You might be better getting the fast 4 hour train to Bangor and a 1 hour bus journey or a flatish 22 mile, 2hour cycle to Trefor! But it’s not a day trip!
So stay over. But worth pointing out here that Trefor is in one of the heartlands of Welsh speaking, in an community that is struggling to maintain itself in the face of massively rising house prices and desperate housing shortage for local people, driven by retirees, holiday homes and Air BnBs. There have been marches this year about this issue e.g. in nearby Caernarfon. 
So if you can, either camp, stay on one of the caravan sites or use ‘private room’ Air BnBs. Or use somewhere like the language centre at Nant Gwrtheyrn 
And remember to ‘siarad cymreig’ in the shops etc, as you would speak the native language in any other country in Europe. Try these phrases! 
Driving – It’s also a long old drive and again not a day trip! There’s parking at the harbour, in the village and above Nant Gwrtheryn
 http://wikimapia.org/20051151/Trefor-Granite-Quarry-or-Yr-Eifl-Quarry  https://www.francisfrith.com/trefor/trefor-the-quarry-incline-c1930_t241501  https://en.wikipedia.org/wiki/Trefor_Quarry_railway  https://canadacurlingstone.on.ca/granite-types/  https://www.thefreelibrary.com/Welsh+gold+at+Salt+Lake%3B+The+curling+stone+that+brought+glory+to…-a083231402  http://www.snowdoniaheritage.info/pdf/pilgrims/pilgrims-nefyn/traeth-trefor-english.pdf  http://resources.hwb.wales.gov.uk/VTC/2008-09/history/stori-chwarel-graiglwyd-the-graiglwyd-quarry-story.pdf
 https://nation.cymru/news/campaigners-march-on-caernarfon-to-call-for-action-on-second-homes/  https://nantgwrtheyrn.org/accommodation/ who may have unused accommodation.