Aug 30, 2011 - 10:02 AM
Hello kmanme, and welcome! If weather is fine, you could get up to the Harder Kulm from Interlaken and enjoy the view up there. You may also manage to make a boat trip over either lake Thun or lake Brienz, if that appeals to you. A short walk along one of the shores would be nice too. This day trip overview
may provide some further ideas, and the timetable
will help you decide which (short) trips from Interlaken are suitable for your arrival day in Interlaken.
Lucerne has lots to offer: the beautiful lake, museums (such as the Swiss Transport Museum or the Glacier garden), a nice town centre, and of course viewing points such as Pilatus and Rigi. You could browse this forum for some more ideas, as there have been previous topics on Lucerne.
I hope this gets you started!