Updated:
Einigen is a small village on the Thun side of Spiez. Its historic church beside the lake makes a pleasant short stop; remember it is a working place of worship when a service or ceremony is taking place. For a longer walk, use marked paths and do not assume the shore is continuous all the way to Spiez.
STI bus route 1 links Einigen with Thun and Spiez. Check your actual stop and the walk from the accommodation, especially for early trains or late dinners. A quiet evening at home may suit you here; restaurant and shopping choices need checking by address.