We start in Gibraltar and take a walk along the beach until we have circled Eurasia clockwise. Which countries do we enter successively until we are back in Gibraltar?
We circle the continent clockwise (The sea is always on the left, the land on the right)
The Suez Canal is considered beach (i.e. we do not enter Africa) and estuaries are crossed by magic ...
Note that we are likely to enter some countries multiple times!
Depends on where you consider the mouth of the Scheldt. Google shows it in Belgium right after Antwerp, Wikipedia locates it in the Netherlands near Vlissingen. I sticked to Wikipedia.