I know of several words for this.
Already mentioned: Boardwalk, wooden (plank) path.
(Boardwalk is, afaik, derived from "walkway made out of boards", board being an old synonym for plank.)
What I haven't seen yet: Log-path or log-road.
These have been in use for thousands of years in European swamps/bogs and were usually made of 4' to 6' sections of log, often split length-wise with the split-side facing up to get a more even surface.
In the Netherlands/Germany they are also known by the term knuppel-pad (Dutch) or Knupfelpfad (German). Knuppel/Knupfel means "big stick of wood" like a bat or a rod. Small log would sort of fit the bill in translation for that.
In modern days the rough logs get replaced by neat planking, but the basic idea is still the same and the name remains.
I have seen the term log-path used in Ireland, Scotland and on maps/signs in Scandinavia, the Netherlands and Germany where a English text was provided for the tourists.
Please note: Log-road can also mean "(temporary) road used by loggers to get access to the forest area where they are working."