Quoits, elsewhere called cromlechs or dolmens, are mysterious structures. Variations of them are found across the whole of Eurasia.
They are often described as chambered mounds that have somehow eroded away, revealing the stones underneath. This is highly unlikely since none of them are half-eroded and there is little sign of where the eroded materials went to. Also, chambered cairns and tumuli don't erode like that, so why should quoits? No, they were built more or less as they look today, when intact.
They are often linked with funerary rites - something which is probably only half-true. That is, sky-burials on top of the capstone and death rituals might have taken place there, but this probably wasn't their primary purpose.
Quoits have a large capstone placed on top of approximately vertical stones, usually with a gap at one end of the chamber inside, or a few gaps, and a blocking stone at the other. Some dowsers see them as earth-energy devices where an up-welling energy-stream emerging from deep in the earth is capped, bent and sent out across the land.
Alternatively an energy-line in the landscape is captured, sending its flow downwards, perhaps, for some reason, to stop its further progress. Or both. Archaeologists disagree, though the alternatives they offer are rather weak - they generally believe quoits are simply denuded graves.
Mulfra Quoit, with fallen capstone
Quoits were probably multi-purpose, and they remain an open question. Conceivably they were used as energy-chambers where illnesses could be treated, seeds could be upgraded, special items could be empowered or spiritual initiations could take place.
Or perhaps in the neolithic cosmology, people felt the earth needed infusing with light or the landscape needed infusing with underworld influences, or an alternating current of both.
In West Penwith, quoits exist only in the northern upland half of the peninsula, with Grumbla Quoit - not conclusively a quoit - placed a distance away from the others. All quoits are mutually linked by three-point alignments involving two quoits and one extra site, usually of similar age. They often have a visible locational relationship with nearby tors or hills.
Nevertheless, some of them are located in odd, non-prominent places. Chûn Quoit is on the side of a hill, and Zennor, Sperris, West Lanyon and Bosporthennis Quoits are a wee bit hidden away, though Mulfra and Lanyon Quoits have fine panoramas. Lanyon Quoit, judging by the major backbone alignments going through it, is geomantically a key site in Penwith, a node for three major backbone alignments connecting stone circles, tor enclosures and cliff castles.
Most quoits are nowadays ruined except for Chûn Quoit, which is in fine form. Mulfra and Zennor Quoits are well worth visiting, though the others are sadly poor reflections of their former selves, nowadays a bewildering rock-pile.
It seems that, except in the case of Chûn and Lanyon Quoits, the quoits have been intentionally decommissioned. That is, the capstone has been lited off and leaned on the side, and one vertical stone has been completely removed - presumably to make re-erection a bit more complex. If one accepts that they had some sort of earth energy-related purpose, then presumably the people who decommissioned them saw them as unwise or dangerous to be left unattended or uncared for.
Lanyon Quoit was reconstructed inaccurately in the 19th Century, no longer resembling its original height and proportions, though it is accessible and still quite alive. Apparently the capstone fell off in a storm.
Impressive in their engineering, quoits were built in the mid-neolithic in the 3000s BCE. Sperris Quoit has been dated to 3600-3300 and Zennor Quoit to 3300-3000 BCE, both being near to each other and also aligned with Lanyon Quoit.
West Laynon Quoit, ruined
Some sites labelled as quoits are not conclusively so - being ruined, it's difficult to tell. These include Grumbla Quoit and Giant's Grave (near Morvah). Judging by their seeming lack of alignment connection with the other quoits, Grumbla Quoit and Giant's Grave might have been something else. Bosporthennis Quoit is linked by quoit-style alignments to other quoits, tending to verify it as a quoit.
West Lanyon Quoit, like nearby Lanyon Quoit, is a node for multiple ancient site alignments. However, Lanyon has a lot of longer-distance backbone alignments, whereas West Lanyon has many local alignments located within the Penwith highlands. They seem to act as a pair.
The quoit question remains open, unhelped by the quoits' ruined state. Yet alignment geomancy gives more clues. More on quoits here.