Swiss pass.

please advise on the area around Interlaken (including the jungfrau region and the mountain railways to the north) where there is not unlimited free travel.

Hi Oapja. You can best take a look at the map we link to at the Swiss Pass page, under the header 'Swiss Pass features'. This map shows the exact validity of the Swiss Pass on all routes around Interlaken. Ongoing lines indicate free travel, dashed lines indicate a reduction. Most mountain trains and cable cars have a 50% reduction; the train heading for the Jungfraujoch from Wengen/Grindelwald is reduced by 25%.

OAPJA
Also the local busses in Interlaken and the Postal Busses in the area are covered with no charge on the Swiss Pass.
Dick