By the second week of the New Year it's a fair bet that any after-effects of New Year's Eve partying will have worn off - unless you're in the Gwaun Valley in West Wales, where you'll just be gearing up for the New Year celebrations in mid-January.
That's because the locals in this secluded valley, between the rolling Preseli Hills and the storm-lashed Pembrokeshire coast, celebrate new year according to the Julian calendar and not the Gregorian, like the rest of us. No idea what the means? Not surprising really, since much of mainland Europe stopped using it in 1582, though Britain didn't drop it till 1752.
But not so for the good people of Pontfaen and Llanychaer, the two hamlets that make up the tiny population of the Gwaun Valley. They continue to ignore the Papal bull that resulted in thirteen days being docked to ensure the accuracy of the Christian calendar, and led to riots around Europe as peasants reacted to 'losing' 13 days of their lives.
The Gwaun Valley celebrations are known as 'Hen Gwaun' in the Welsh language. Len Davies, the owner of the tiny local brewery, points out: "It's been a long tradition for many of the farmhouses in the area to host a party", while celebrations also take place in the valley's two pubs (in Pontfaen the pub is the front room of Bessie Davies' house, and the beer is served through a hatch from a jug dipped straight into the barrel).
The fact that the 21st century (along with the 20th, 19th and 18th) hasn't gained a secure foothold in this lovely corner of Pembrokeshire is apparent from more than just the arcane New Year celebrations.
The valley's dark woodlands have a mystery to them at this time of year that isn't felt in the more bucolic summer months, perhaps partly explained by the presence of the Preseli Hills.
The hills were a stronghold of the ancient Celtic tribes who once lived here, and home to monuments such as the spectacular Bronze Age megalith of Pentre Ifan, some 6000 years old. More enigmatically, bluestone blocks were quarried from the hills and transported 400km east to make up part of Stonehenge. How this was done is still a mystery.
You can immerse yourself in all this history in just one day - but why not give yourself a little more time in this lovely region of Wales and take part in one of the world's more bizarre New Year celebrations too?
Out and about
Pembrokeshire has some of the finest sea kayaking in Europe - local guide Nige Robinson can help you explore its cliffs, beaches and islands.
Get a good wetsuit and hit some of the quietest waves in Britain along the Pembrokeshire coast. Boards and wetties can be hired at Ma Sime's Surf Hut in St David's.
The Golden Road is an easy-to-follow 12km Bronze Age trading route, which takes you across the spine of the Preseli Hills and provides a panorama that on a clear day can take in much of Wales and even the Wicklow Hills of south-east Ireland.
You can also mountain bike along the Golden Road, while the quiet country lanes of this part of Pembrokeshire are great for road cyclists. Bikes can be hired at Pembrokeshire Bikes in Fishguard.