Please, what is the best transportation to travel from Spiez to Oberhofen Castle on Lake Thun? Thank you!
Google maps shows a combo of train and bus possible. See this link https://www.google.com/maps/dir/Spiez,+Switzerland/Oberhofen,+Switzerland/@46.7218225,7.6499239,13z/data=!4m12!4m11!1m2!1m1!1s0x478fadd623415365:0x3d8e3909f94b4d91!1m2!1m1!1s0x478fb20a290391d3:0x609b256178f8d463!2m3!6e0!7e2!8j1551952842!3e3.
Rome2Rio also adds in the ferry possibility https://www.rome2rio.com/s/Spiez/Oberhofen.
According to SBB: https://www.sbb.ch/en/
Spiez to Oberhofen am Thunersee (there is more then one Oberhofen in Switzerland), lots of options shown, train to Thun then bus, or bus+bus.
However Spiez and Oberhofen are on opposite sides of Thunersee. So, depending on the time of year, I would take a lake boat in at least one direction.
Info here: https://www.bls.ch/en/fahren/unterwegs-mit/schiff