There aren't many better feelings on a bike than getting to the top a gruelling climb. It might feel like searing hot pokers are being jammed into your thighs and that a particularly cruel and invisible giant is squeezing the air out of your lungs on the way up.
But when you get to the top, it's almost always completely worth the effort. Plus, you get to ride back down again.
Getting the miles under your belt on the flat with a nice tail wind is all well and good. But the best cycling holidays are all about achievement. And being the king or queen of the mountains is about as good as it gets.
Climb are what make the mountain stages of the Tour so compelling, and they are what keeps us getting back on the bike and heading out in the wind and rain for the nearest spot of nasty elevation.
You might think you've taken on a few climbs in your time. But this list of the top 10 toughest climbs is in a different league. If you've managed any of these, then give yourself a pat on the back because you, my friend, are one tough cookie.
Mont Ventoux, France
Described by the legendary/disgraced (delete according to personal preference - I'm not getting involved) Lance Armstrong as the 'toughest climb on the Tour bar none', you know this is going to be hard. The climb is 1,600 metres over the 22 kilometre section and there is not one single flat stretch to give your aching muscles a break. Cripes.
Pang La Pass, Tibet
At 20 kilometres long and climbing 1,000 metres, this may be shorter and shallower than Mont Ventoux but this mother is not covered in tarmac. That's right, this is a soul-destroying ride through gravel, shingle and all sorts of other muck. Not for the feint hearted or anyone without the right bike.
Lagos de Covadonga, Spain
Not the longest climb but mighty steep, this little swine has two particularly tough spots - the nasty ramps at La Huesera and the Mirador de la Reina. Fortunately, the climb is made a little easier by the stunning scenery of the lakes below. Not that you'll care about them when your eyes are popping out of your skull due to exhaustion.
Mur de Huy, Belgium
How bad can a 1.3 kilometre climb be in Belgium, one of Europe's flattest countries? That's what so many people ask themselves. The again, just as many wish they hadn't been so bloody stupid immediately afterwards. Maybe it's the fact that it's preceded by so much even terrain that makes these two minutes some of the worst in your life.
Great Dun Fell, Cumbria, UK
Known to some as our Mont Venoux, this is widely regarded as the toughest climb in England. It might be a private road but there are no objections to cyclists riding along it. The radar station's 'golf ball' sits atop this 40-minute climb, taunting you by never seeming to get any bigger.
Alpe d'Huez, France
Another legendary French climb that is well known to serious climbers. But, as they say, familiarity breeds contempt. This may be a spectacular alpine ascent but the instant the 13% climb hits you straight in the face, you'll wish you weren't cycling in France but somewhere else. This is 13 kilometres of hairpins and long, nasty straight climbs.
Stelvio Pass, Italy
The highest paved mountain pass in the Eastern Alps and second highest in the Alps themselves, this is a serious climb. Originally built to connect the Austrian province of Lombardy with Austria itself, about halfway into this one you will really be wishing they hadn't bothered.
Lhaka La Pass, Tibet
This is on a par with the Pang La pass mentioned earlier but by virtue of being paved, this is slightly easier. Although, easy is not an adjective we would like you to associate too closely with this absolute monster of a climb. At over 5,000 feet in altitude, the thin air makes this one even more of a lungbuster. No one can enjoy this climb, can they?
Onion Valley, USA
This climb may be set against the backdrop of some of the best mountain scenery anywhere in the world. But you know what? It's still doesn't make it any easier. This near 700 metre vertical climb is grim and gruelling. The fact that it is possible average well over 50 kilometres per hour on the way back down should tell you everything you need to know.
Mt. Washington, USA
The myth, the legend - this is often described as the world's toughest climb. And to be honest, it's hard to argue. At nearly 12 kilometres long and with an average gradient of 11.8% (that's average, people) this is frankly a terrifying prospect. But that's not all.
Only about two thirds is paved and vicious winds and near freezing temperatures make this something only a fool would attempt. Apparently it all used to be paved but some bits of it simply washed away because it was too steep. The very fact that might be possible should be enough to put most people off. And yet, still they come.
If you can take on any of these then, as Rudyard Kipling said, you will be a man, my son. A battered, whimpering broken man.
But you can't have everything can you? Climbing on a bike is not just about numbers though. The steepest hills are not always the worst. Sometimes it is the length, the false sense of hope or the face-slapping head wind that makes a climb really bad.
Getting to the top of any hill on road cycling holidays, no matter how small, is always an achievement. It's conquering the biggest obstacle of all - your own mind and body's desire to stop. If you can beat yourself climbing a hill, then it feels like there is nothing you can't do. And as feelings go, that's a pretty good one.