Brussels, Grand Palace, Bruges, Antwerp, Netherlands Amsterdam, Den Haag, Rotterdam, Paris (One Night Journey), Switzerland (Lucern, Interlaken, Zurich)
Austria Zell Am See, Vienna
Spain Barcelona Madrid
Rome Italy Venice Milan
Germany Berlin, Dusseldorf (A day trip from Amsterdam)
Denmark Copenhagen You can plan to take early morning flights to travel to next countries.
Make sure u include Lucerne in your Switzerland Itinerary... Its an amazing place...We had also visited Paris, Amsterdam & Brussels/ Brugge in Belgium which are well connected with Switzerland and some of the closest places and definitely worth the visit.
You can visit Paris and Germany
however don't club too many countries in a trip ,I would suggest
Switzerland itself is a grandiose country
Interlarken would be the best base in Switzerland
it has many activities like paragliding, cycling, rafting etc