Puente Viesgo

The first thing you notice is the smell of butter and lemon drifting from the bakery on Calle Real. Only afterwards comes the realisation that the pavement is warm even though the Cantabrian sky is the colour of slate. Puente Viesgo sits low in the Pas valley – 80 m above sea level, not the 800 you half-expect in northern Spain – and the Gulf Stream keeps the air mild enough for palm trees beside the river while the peaks behind still carry snow.

This is a working village of 3,000 souls, not a postcard. Lorries rumble over the 16th-century bridge because the N-623 is still the most direct route from Santander to the industrial towns of the interior. Park on the eastern bank, feed the meter €1.20 for two hours, and everything is within a five-minute radius: the caves that got UNESCO excited, the spa that opened in 1886, and the fisherman’s path that ducks under the main road and disappears into hazel woods.

Up the hill where the mammoths once were

Monte Castillo rises 200 m above the rooftops, a limestone ridge drilled like Swiss cheese. The Cueva del Castillo and the smaller Cueva de Las Monedas are the only two you can enter; both close on Monday and Tuesday outside July and August, and both sell out at weekends even in April. Reserve the night before on the Cantabrian heritage website – the system is clunky but it works – and arrive ten minutes early or the guide starts without you. Entry is €3, less than a flat white, and the tour lasts 45 minutes. Inside, the lights snap off between stops to protect the art, so the 40,000-year-old hand stencils suddenly glow red as if someone had just blown pigment on to the wall.

The walk up is steep enough to raise a sweat, though the guide will wait if you’re only slightly late. Trainers suffice; sandals do not. Once the iron gate clangs shut the temperature holds at 13 °C year-round – bring a thin fleece even when it’s 30 °C in the square. Photography is banned, a relief in a way; you’re forced to look instead of lining up selfies.

Las Monedas is the quieter sibling, all stalactites and a single etched horse that stares out from a calcite curtain like a ghost in the headlights. If you manage the double bill, allow ninety minutes between tours for the descent, a coffee and the climb back up.

A river walk that ends in cake

Back in the village, the Paseo del Pas is flat, push-chair-friendly and signed 1.5 km each way. Ducks nest under the railings and old men cast for trout where the water slows. Turn left at the picnic tables and you reach a waterwheel that once drove the spa’s hydropathy pumps. Turn right and you hit the municipal pool (summer only, €2.50) and the green-way cycle path that follows the old railway to Santillana del Mar – 16 km of tarmac with no hills, ideal for families. Hotel Pasaje rents bikes for €15 a day; ask for a lock because bike racks are rare once you leave the valley.

The reward for any of these gentle exertions is the bakery product that travelled the other direction. Sobao pasiego was invented up in the mountain cabins as something that would keep shepherds going for a week; here it is served in thick slices with coffee for €1.80. The texture is closer to pound cake than sponge, the crust glazed with egg so it freckles in the oven. Locals dunk it in black tea, builders dunk it in cortado, and nobody judges either way. If you prefer savoury, the market bar does a bocadillo of grilled Pas salmon – river fish, not farmed – dressed only with olive oil and a squeeze of lemon. It arrives with the tail still on, proof it was swimming that morning.

Thermal water and Victorian tiles

The spa building looks like a miniature casino, all wrought-iron balconies and green tiles. Inside, the 28 °C pool is free if you’ve booked any treatment; otherwise it’s €18 for a 45-minute soak. The changing rooms are 1950s functional, but the water is the real thing, bubbling up from 800 m down with enough sulphates to smell faintly of struck matches. British visitors tend to arrive expecting Champneys and find instead something closer to Harrogate in 1938 – elderly Spanish ladies doing breast-stroke in pearls, and a notice asking you to shower before and after. Treatments start at €32 for a half-hour massage; book the day before, especially at weekends when half of Santander drives up for the day.

Across the road, the church of San Miguel hides a baroque altarpiece gilded with American gold. The door is usually unlocked; drop a euro in the box and the lights flicker on like a theatre curtain. The heraldic shields on the surrounding mansions are worth a slow circuit – look for the one with a lion wearing a bishop’s mitre, the mark of a 17th-century cleric who never quite gave up family life.

When the valley turns green and loud

Spring arrives early; by March the meadows are neon and the first tractors cut silage at dawn. This is the best season for walking to the cabañas pasiegas, the stone huts with thatched roofs that dot the hillsides above the village. Follow the track past the cemetery and you reach three of them in 40 minutes; keep going and you can loop back via Vega de Pas, 8 km in total. After rain the path is a clay skating rink – proper boots, not country-park trainers, are essential.

October brings chestnut fairs and the quesada pasiega, a baked cheesecake sold still warm in brown paper. The valley quietens after Spanish half-term; hotel prices drop by a third and the caves feel half-empty. Winter is misty and short – daylight gone by 6 pm – but the spa steam rises into the floodlights and the bars still serve cocido montañés, a mellow bean stew that tastes of bay leaf rather than chilli. Ask for it on Wednesday, market day, when the square fills with pop-up stalls selling smoked cheese and socks.

How to do it – without the face-palm moments

Puente Viesgo is 25 minutes by car from Santander airport. Avis and Europcar desks sit in the terminal; if you’re relying on public transport, ALSA bus line 120 leaves Santander at 09:15 and 19:00, costing €3.65. There is no train. Once here, cash is king – the only ATM is outside the Gran Hotel on the main road, and it runs dry on Saturday night. Most bars close by 10 pm; stock up on water before 9 if you’re staying in an apartment.

Do not confuse the local caves with Altamira, 15 km away and visitable only by lottery twice a week. Do not expect a beach – the coast is 30 minutes west, so tag on Santander if you need sand. Finally, do not turn up at 11 am on Sunday hoping to slip into the next cave tour; you will join a queue of thwarted day-trippers and the nearest plan B is a 40-minute drive. Book ahead, walk slowly, and leave room for cake.