Hi emihalick, Assuming that you'll be traveling quite a lot during those 21 days, a single ticket Paris - Geneva plus a 22-day Swiss Saver Pass would fit your needs. Please check this FAQ for more details on how to select a pass.Have fun!
All you need to know about traveling by train, bus or car in Switzerland.
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Swiss Travel Pass promotion 25% discountOnly if purchased in July 2021. Free cancellation.Buy via the SBB travel centre at https://shop.switzerlandtravelcentre.com or HappyRail at https://www.happyrail.com/swiss-travel-pass.