First time in Switzerland

There are no direct trains to Brussels from Switzerland, the best you can do is a single connection. There are three from Interlaken Ost, Bern, and Basel with a train change in Frankfurt. There are more options from Basel with single change in Cologne. There is also Paris, but that requires a station change from Gare de Lyon to Gare du Nord.

Do you have a specific destination in Switzerland in mind?

Never having been to Switzerland we are open to suggestions about what we should see.

Seems like some unnecessary long travel here. Is there a reason you are not doing Paris-Brussels-Switzerland, or better yet, Brussels-Paris-Switzerland?

We have a round trip ticket to Paris and so we are making a circle, Landing in Paris, south to Switzerland, north to Belgium, and finally back south to Paris. We could go clockwise or counter clockwise. We choose the latter. Any particular things in Switzerland that you can recommend?

Luzern and the Berner Oberland are always popular. 3 nights in Luzern would give you 2 full days, then 3 or 4 nights in the BO. Wengen or Muerren would be my choice.

The train to Switzerland from Paris should be fairly easy, depending on where you go. Basel and Zurich; no problem. You might want to consider staying on the south end of Lake Konstanz, which gives you the Alps, and the lake for activities. Lot's to see and do there.

You may also want to consider flying to Brussels from Zurich. The flight is only a bit over an hour vs the whole day you'll lose via train.

Look on YouTube to get an idea of the attractions fitting your likes. Pick a few (not too far apart) and fill the rest of the time experiencing the views. Consider the weather could be raining or foggy, plans need to have flexibility.

First of all do not be to set on direct trains. Changing trains is a normal and expected feature of train travel. You can book a ticket from Paris to pretty much anywhere in Switzerland on www.sbb.ch, but most destinations will indeed involve a change of trains. These are trivial and easy.

There are unfortunately no longer any direct trains from Switzerland. They fell victim a few years ago to SNCFs obsession with high speed trains. Maybe we will see their return one day. Until then you either have to backtrack via Paris, or go via Germany. I do this trip quite regularly and always go via Germany. But you may want to look at a flight as well.,