The Custom House:
Queen Elizabeth I granted Gloucester the formal status of a Port having its own Custom House; so that vessels trading with other countries could load and discharge their cargoes.
The Custom House was used throughout the 17th century and the early part of the 18th. Since then, it has used for a variety of purposes and is currently offices - I think?
I'm pretty sure that in recent times, it served as a Wine Shop/Bar, which appears somehow appropriate!
The Old Quay:
Evidence of Roman Quay walls were discovered in 1846, along with Saxon and Medieval quaysides along the old east channel.
In 1580 the quay, known then as the king's quay, was designated the principal landing place in the new port of Gloucester. Further construction of a second quay extending southwards was completed in 1623.
At the time the path of River Severn came very close to St Oswald's Priory and there was a small amount of 'business activity' there.
With the establishment of the Custom House, the Port of Gloucester became a busy commercial centre and the quay, a hive of activity.
However, the opening of a direct overseas trade by way of the river in 1791 gave impetus to the construction of a ship canal terminating at a basin or dock on the south side of the city. This became the Gloucester to Sharpness Canal.
The obvious result of this was inexorable decline of the old quay which continued to be used only for private ‘wharfage’.
The Custom House was moved to the new Docks and weirs were constructed at Llanthony and Maismore, causing the east channel to silt up; this sealed the fate of the facility once and for all. By the end of the 1800s, it was defunct.
The cache location is right opposite the Old Custom House and close to where vessels would have been exchanging goods nearly 2 centuries ago.