That's an awesome trip but I think a bit more research will help you improve your plans.

There is no ferry from Magadan to anywhere.

There are cargo boats that transport vehicles to Vladivostok, in the summer navigation season. You might get to P-K via Vladivostok on a cargo boat (though you will most likely have to fly separately), from Magadan I very much doubt it (who would want to use that route?).

Leaving St P in September, if I understand correctly, will give you very little time to spare en route. The pinch point is crossing the Aldan river between Yakutsk and Magadan. In summer it is a 1 hour ferry, in winter you drive on the ice road. There is however a period between the first ice forming and the ice being firm enough to drive one when the route is totally impassable. The freeze starts usually in mid October. In 2017 I crossed the river by ferry on something like the 3rd October. 10 days or 2 weeks later the service stopped. Obviously this date is down to nature and could be earlier or later. You could certainly make it, but you will have very little time to spare on the way. Or, if you are prepared for serious cold, the trip is much more interesting in winter, but it can be late November by the time the Aldan river freezes up enough for the ice road to be opened.

The Altai region is a mountainous area shared between Russia, Mongolia, Kazakhstan and China. It is about as remote from the ocean as you can get and is most certainly not a peninsula.

Interested to see whether you can cross the land border. As I understand, citizens from certain countries can still visit Russia on a tourist visa but it's not clear if this is only for arrival by air. Hope you make it, please keep us informed!

EO

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EurasiaOverland a memoir of one quarter of a million kilometres by road through all of the Former USSR, Western and Southern Asia.