Hi. I am planning Europe Vacation for 2 weeks in late April which should cover Amsterdam and other places for 2 weeks which we have in hand.

I have already visited Switzerland, Spain, France. Therefore other than these countries what countries you can suggest to visit

My son who is 23 years old would like some bustling cities and some adventure whereas we couple would like some serene places full of nature

As per above what itinerary we should plan for 2 weeks. Your suggestions will be very useful in planning further.

Thanks in advance

This is not how a forum like this works.
You, after doing some research come up with a basic itinerary . We then can help fill in the gaps, usually add a treasure or remove something that is or could be a waste of your time.
Transportation is a factor we need to know about. Plus port of entry and exit.
Note that every city is bustling !
What do you call adventure? Going down to the "hood" or taking a zip line, riding a bike in Amsterdam maybe?