Considering the Ana's Cottage in Cascais?
A VT member wrote the following comment about visiting Cascais:
Forte de Cascais by ncfg
The Cidadela or the Fort of Cascais is dated from 16th century and it was built to protect the Bay of Cascais. It is part of a whole line of fortresses along the Tagus River that were built to protect Lisbon from being invaded.
From there you can appreciated a lovely view.