What is the fine-grained topic of the following text: If all goes well - if Stefan doesn't fall into the cold waters of the Manukau - then visitors to the underpass will be able to haul a geocache up from empty space between the bridge and the harbour, and examine a collection of artefacts of the epic strike that delayed the construction of Mangere's bridge for two and a half years at the end of the 1970s. Only return the topic.
Geocaching at Mangere's bridge related to epic strike in the 1970s