Possible scenarios to play:

* Create BOB (Interlaken - Grindelwald - Lauterbrunnen)
* Create SBB / BLS lines (Thun - Spiez - Interlaken)
* Create Brienzersee line (Interlaken - Meiringen - Brünig)
* Connect the Valais to the Bernese Oberland (Thun - Spiez - Brig)
* Top of Europe: Connect Grindelwald & Lauterbrunnen with the white mountains Eiger / Mönch / Jungfrau (Steep! Maybe only nicely doable with Trams instead of train)
--> Note: Also you would need to place a "Hotel" or similar to attract people on the mountain!