This is not a journey as such but a change of name. Shire Hall used to be the home of Berkshire County Council but is now occupied by a private company, who changed the name to Shinfield Park. For parking I suggest you park at the nearby housing estate also known as Shinfield Park. You cannot park at the former Shire Hall, (unless you are an employee of course). Alternatively the No 9 bus stops right outside Shinfield Park.
To retrieve the cache you'll have to solve a puzzle. It's sort of related to the new occupants' line of business. Shouldn't be too difficult for those with either a chemistry background or access to Wikipedia.
N 51 (ethane)(butane).(nonane)(butane)(octane)
W 000 (pentane)(heptane).(zero)(heptane)(propane)
Dependent on the time of day you will need extreme stealth to retrieve this cache as its near a busy junction.