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Interlaken is useful when a short stay branches in several directions. Check the station, though: trains into the Grindelwald and Lauterbrunnen valleys start at Ost. Lake Thun boats use West, while Lake Brienz boats use Ost. The two lakes do not share one through boat service.
Leave a little time for the town and a meal, not just the next departure. Central streets can be busy, but that does not describe every address. Being between two lakes does not guarantee a lakefront hotel, either. The homes listed on this site are around Lake Thun; include that journey when comparing a stay.