If you feel like taking a walk after lunch at Saint-Cergue.. there is a walk you can take, called 'le sentier Ballade à Béatrix'. It is welll indicated, with 16 points of information. It starts with a little steeply, but the forest is very pleasant, the views from the old castle are impressive, the invisible ruins, and it goes through a series of rocky formations with interesting caves.
A simple route, strongly recommended, with very little uphill.
We start at the camping place of Vallorbe, with a strong vertical slope untin we cross the col. From there, we descend through a minor road until Vailion. After crossing the village we enter once more at the forest, where we cross a defensive system (the toblerones) where we start once more to descend, following the river. In the last part, we walk next to the river and cross wooden bridges several times.
Via ferrata at the foot of Pedraforca. There are three tracks, one for children, and two more serious ones. The first is a bit difficult, the second one has quite a bit of overhang, as well as overhang at the descent - it is only recommended to those with experience and arm strength.