A two-staged multi at the historic Ancaster Mill. The posted coordinates will take you to a historical sign in one of the parking lots for the Ancaster Mill where you will need to do some simple research and some quick math to calculate coordinates for the final. Cache is a bison tube with only a log and is located in the Mill area.
To calculate the final:
NORTH
From the sign at the posted coordinates:
a) Read the first paragraph and note the year of the historical event that took place as a result of the investment scheme at this location
b) Find the year at the very bottom (center) of this plaque. Subtract a) from b). You will have a 3 digit number with a checksum of 11
c) Divide your answer by 2 then subtract 36
d) Divide that number by 1000 and ADD it to the posted North coordinates
WEST
When you turn around from reading the historical sign, you will observe a bridge near the entrance to the chapel that leads you across the creek
a) Locate the 'name' of the bridge (5 letters)
b) Convert the letters to numbers (a=1, b=2 etc). I have provided a conversion table in the picture gallery if you don't feel like counting your fingers :-)
c) Add up each of those five numbers to get a two-digit number. ADD 15 to your answer
d) Divide the result by 1000 and SUBTRACT it from the WEST posted coordinates.
Go get the cache. Stealth required.
HISTORY LESSON
There have been four different mills built in this area - three on this exact site. The first three were destroyed by fire. The current building dates from 1863. A recent image of it is shown below: 
FOUNDING OF THE MILLS
Ancaster is notable for being one of the oldest settlements in Ontario. James Wilson along with his affluent fur trader, entrepreneur and business partner Richard Beasley, were the primary founders of Ancaster village. Together they chose to build a gristmill and sawmill at this location in the late 1700s. The main street in Ancaster is named after him, and in fact the area was first known as Wilson's Mills.
This site provided accessible water power (Ancaster Creek) at the juncture of already well-established pre-historical indigenous transportation trails. Wilson built a gristmill in 1791 and a sawmill in 1792 that would be the only mills west of Grimsby for many years.
In that period the area was populated with just a smattering of First Nations aboriginal peoples and wilderness farmers. In order to attract workers to his mills, Wilson needed to attract workers to an isolated area of frontier forest. Wilson and Beasley managed to generate the impetus for a community by constructing a general store, a blacksmith shop, a distillery and a tavern all within walking distance of his mills (All around the area of this geocache). As a result, Wilson's newly arrived employees began to build their homes here. To this day, the main street that winds through the historical Ancaster Village that once was a section of the original aboriginal Iroquois Trail still bears the legacy of Wilson's name.
Below: The Ancaster Evaporator, (circa 1899) stood where Wilson's original gristmill was located at the north-east corner of Wilson and Rousseaux St (the small wooded area at the traffic lights). The foundation is supposedly still visible there. 
NAMING OF ANCASTER
By 1793 an area of land that contained Wilson's Mills was finally surveyed and officially came to be known as Ancaster Township as chosen by John Graves Simcoe. He was apparently inspired in the name choice by Peregrine Bertie, the 3rd Duke of Ancaster and Kesteven. Thus, Wilson's Mills was indirectly renamed Ancaster after an ancient village and former Roman town that stills exists in the district of Lincolnshire, England.
Below: A view from just out on the street (Old Dundas Rd) near the posted coordinates. The water is the old mill pond. The building in the foreground is a the old tollhouse at the corner of Wilson St and Old Dundas Rd. A white fence is running along the side of Wilson St. The long dark building at the left edge of the picture is the Ancaster Evaporator pictured above. 
In 1794, Wilson sold his half share of the grist-mill and sawmill business to Montreal-born fur trader, interpreter, businessman, militia officer and office holder Jean Rousseaux who already had a home and general store on Wilson Street. Rousseaux's Ancaster general store experienced frequent trading with Joseph Brant's Mohawks and other Iroquois people from the Six Nations confederacy located at the Grand River.
A THRIVING COMMUNITY
By 1823, due in large part to its easily accessible water power located at the juncture of already existing historical trading routes, Ancaster had become Upper Canada's largest industrial and commercial centre. Additionally, Ancaster had at that time attracted the 2nd largest populace (1,681) in Upper Canada trailing only Kingston (population 2,500), but surpassing the populations of nearby Toronto (1,376) and Hamilton (1,000).