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Without considering other factors (links, domain age etc), your understanding certainly ties in with one of the front runners in the industry who use

domain/activity_name/category/subcategory/activity_reference

We have over 2000 non branded experiences and activities sold through our website.  The website is having a face lift with the a new look and a stronger focus on SEO.  As part of this, I am keen to establish what the best practice is for product based URLs.  I've researched the market and come up with a few alternatives that are used:

domain/category/subcategory/activity_name

domain/activity_name/category/subcategory/activity_reference

domain/generic_term/activity_reference/activity_name

domain/category/activity_location/activity_name

Activities are location based but the location can change (say once every 2 years).  Activity names, category, subcategory and activity_reference rarely change.

Are there any thoughts/ research on the best method?  (If there is one)

Many thanks in advance for your insights.

I think if it is outdated and it is not maintained then it may be creating unnecessary focus and wasted energy.  I'd suggest taking it down until it is updated.  Perhaps in the meantime replace it with a top 10.