I wouldn't agree with Craig Weatherhill, in "Cornovia: Ancient Sites of Cornwall & Scilly" (Cornwall Books - 1985, revised 1997 & 2000) who says the best place to view the dyke is where it abuts the south side of the road between the west side of St.Agnes and Goonvrea (at about SW717501). Yes, there is a public footpath at that point but it is separated from the dyke by highish hedge, and there is no obvious way to see the dyke close up.
I didn't try viewing the bank (up close) from a different place. The obvious place to try would be where the bank crosses the road from St.Agnes Beacon to Towan Cross (around Goonvrea Farm, at SW 713496). Instead, I got a pretty good overview from the top of St.Agnes Beacon although it does take a few moments to get your bearings; the dyke is hardly the Wall of China and takes a bit of spotting.
It is believed that originally this Dyke enclosed the whole of the coastal area around the hill, cutting it off from the surrounding land. The reason for the bank is not obvious, and nor is the date. Craig Weatherhill, in Cornovia, writes that "It could date from anytime between 500BC and 1000AD, but opinion leans in favour of a post-Roman date, probably fifth or sixth century AD".
The village of St.Agnes still holds a 'Bolster Festival' in April / May. This consists of two weeks of celebrations in the village including workshops, culminating in a weekend to celebrate the rise and fall of the Giant Bolster. First a lantern and torch procession through the village to the top of the St. Agnes Beacon and a large bonfire and barbecue. Then the next day witness the deeds of the giant revealed in street theatre and dance, before a colourful procession of giant moving puppets to the cliff top at Chapel Porth where the wicked giant was tricked into death whilst proving his love for Agnes.
For the latest info contact St Agnes Tourist Information Centre: Tel - 01872 554150 / Web - www.stagnes.com
A popular story connects St. Agnes with the giant Bolster. This relates how, in order to rid herself of his persistent wooing and the countryside of his tyranny, she (St. Agnes)challenged him to fill a small hole in the rocks at Chapel Porth with his blood as a token of his love. To this the giant agreed, not knowing that the hole emptied into the sea, with the natural consequence that he bled to death!
The hole at Chapel Porth still retains the evidence of the truth of this tradition in the red stain which marks the track down which flowed the giant's blood!
Craig Weatherhill and Paul Devereux, in 'Myths and Legends of Cornwall' (Sigma Leisure, 1994) believe that "Bolster is a good example of a giant being named after an earthwork, in this case the Bolster Bank which runs from Chapel Port to Trevaunance Cove, thus enclosing a large area of tin-rich land including the entire hill of St.Agnes beacon. The bank is now interrupted in a number of places and an isolated fragment immediately south of Bolster is a contraction of 'both lester' (boat-shaped hump)."