If you land at the Euroairport Basel/Mulhouse/Freiburg or if you travel by train from within Europe via Basel, you can reach Locarno by train.
There are connections every hour either direct or with at least one change. The trip takes approximately 4 hours.
Advance booking of train tickets within Switzerland is possible but not obligatory.
On the SBB webpage you can find the most convenient train schedule for you.
Once in Locarno, continue to Monte Verità by following the directions given.