Hope you enjoy Chamonix. Do make sure you take the kids on the Summer Luge.
Oh yes, great fun - but do remember that "Freinez!" is French for "Brake!" not "Duck!" - unlike my mate Ben when we were there many years ago. The braking mechanism is operated by pulling back on the lever. Pushing forward, as you do when you duck, just makes you go faster...
On the positive side, Ben learnt several new French curse words from the person on the luge in front of him.
Annecy is also well worth a visit while you're in the area - in fact, Annecy-Chamonix is an outstandingly beautiful cycling route (including the Col de la Croix Fry - a challenge but not one of the tougher Alpine passes - not to be confused with the evil Croix de Fer).
Apart from that, I second the recommendation for the toll-roads. They all have perfect surfaces and are well worth a few extra quid.
I know it's too late this time, but I would definitely recommend the tunnel next time. It's not just the crossing itself where you save time (30 minutes compared to over an hour [IIRC] on the ferry) but there are trains every 15 minutes, which means turnover is much higher, you can check in later, queues are fewer and shorter, boarding and disembarkation are much quicker (not least because unlike the ferry you stay in your vehicle once you have boarded) and the whole experience is generally much more pleasant. Having used the tunnel a few times, I don't think I could ever go back to the ferry - the only thing I miss about the ferry is standing on the deck and feeling the sea spray on my face.
Yes, the tunnel occasionally closes due to fires and whatnot, but the ferry also occasionally closes due to French farmers and whatnot.
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