Former Russian oil tycoon Mikhail Khodorkovsky has arrived in Switzerland from Berlin, where he's been staying since his release from prison last month.
He travelled by train with his two sons, who were returning to their Swiss school.
Mr Khodorkovsky, 50, was released on 20 December. He spent 10 years in prison after being convicted of fraud, but has always insisted his conviction was politically motivated.
Switzerland granted him a three-month visa after he was pardoned by President Vladimir Putin in a deal that Germany helped arrange.
On Sunday he told Swiss TV he wanted to campaign for the release of prisoners.
You can't remain quiet when you know that political prisoners languish in jail," he said.