The Bidston Gunsite still has the gun placements/holdowns and some remains of the ammunition lockers, one has recently been destroyed but the other may remain, I haven't checked.. Its a bit awkward to get to.
https://www.google.co.uk/maps/@53.4076601,-3.0806078,82m/data=!3m1!1e3I think that is it for accessible gunsites on the Wirral.
The Puddington gunsite is very well preserved but very heavily overgrown and you
MUST ask permission to access it do to the nature of the business that owns the site, if they agree for you to visit you have to sign a disclaimer that basically says if you die even if it is due to their business they are not liable.
https://www.google.co.uk/maps/@53.2523498,-2.9975718,140m/data=!3m1!1e3There are bits and pieces of control centres belonging to the old decoy sites which are accessible.
There are a number of air raid shelters, the massive ones (Bidston and Tranmere deep level shelters) are not accessible but some small ones are.
There are also quite a number of pillboxes as well, at a guess around 20 - 25, I've not actually counted the ones I've been to.