Two conceptually connected walks:

From sea to sea
A walk from Newcastle upon Tyne to Bowness-on-Solway (UK),
from the east coast of England to the west coast of England:
land on my left and land on my right side.

From land to land
A walk along the Afsluitdijk (NL),
from Den Oever on the east coast of North Holland to Zurich on the west coast of Friesland:
(sea) water on my left and (fresh) water on my right side.