When you take the train from Bern to Zürich, you will see Aarburg just before Olten. And the Castle and Church just look so magnificent.
And when you travel by car you will pass the powerstation Ruppoldingen and the Auenlandschaft.
The closest trainstation is Aarburg-Oftringen. From there hike westward. I stay first on the north side and crossed the river in Ruppoldingen and hiked back on the south side of the river.