You can use the new 'Markers' feature. This is a method that allows us to add our own POIs to either a route or a map. A variety of labels can be attached and there is space for notes. 

You'll need to find the POIs -but you seem to be already doing that. As a subscriber, you can gain access to extra maps (website & app). I believe the IGN maps are best for highlighting POIs making life easier for adding markers.

For example, here is a zoomed in section of IGN in Spain

Here is an example of my POIs, mainly campsites but other labels are possible

Thanks for the suggestion. 

You write "As a subscriber, you can gain access to extra maps (website & app).", which I may not fully understand. You mean that I can change cycle.travel's map layer (using the card deck icon top right) that will display POIs such as IGN?

Yes, we can change the map layer using the card deck icon on the top right.

Subscribers get to see more map styles, notably Ordnance Survey in Britain and IGN in Europe.

I'm not sure "display" is the correct description for the POIs on maps. If the map shows POIs then we can see them. They are not 'clickable' unless we place a marker on them. 

Other map styles, such as OpenCycleMap will show bike paths and routes. 

This is NL/Belgium on OpenCycleMap