To me, it sounds like you need to setup a conditial dropdown
Site and Area should be pulled out in to Tables of their own instead of fields on a single Table.
Then Relate Sites can have many Areas
Then Location can go away. (I don't think you'd need it)
To Confirm, when you say
"The relationship is one LOCATION to many WALKS."
Would it be the same to say a Walk can have many locations?
If so, Then you should also do Walks can have many Sites & Walks can have many Areas.
Then use the Conditional Drop Functions of the Key Field (Related Area) of the Relationship between Areas and Walks.
You could then you Related Record ID's to Filter Forms.
IF the Related Site 1 and Related Areas related to 1 are say (3,8,10,12)
Show these Questions, and so on.
I'd be happy to schedule a meeting with you to discuss how all of that would work.