There are two 'Agassiz' rocks on the route - Little Agassiz, which is the top of the hill and is a specific rock, but is part of a bigger area of rocks to hang out at, and Big Agassiz, which is a giant boulder by itself in a swampy area down the trail a bit from the top. Big Agassiz is usually not directly accessible because of water/mud, but on during a dry day you might be able to get there - usually you just hike past it. Yesterday I headed up to Little Agassiz first - there were two dudes climbing it, so I headed down the hill a little ways to a smaller boulder I like to climb & sit on. There is a very nice view from the top of this boulder and skyscrapers in Boston are even visible on clear days. I basked in the sun for a while, took some pictures (mostly just playing with the settings on my SLR) then hopped off and walked down via Big Agassiz.
(top: Boston skyline [squint! It's there!], middle: perched on my boulder, bottom: Big Agassiz)
I hiked down to the car and, realizing I still had time, decided to check out the trails off the parking area I use (on the opposite side of the road from Agassiz Rock), which I'd noticed before but never checked out. A sign informed me this was wilderness conservation area owned by the Manchester-Essex Conservation Trust, which I'd never heard of before. They own almost 1000 acres of land throughout Essex and Manchester with miles of trails through a swamp and woods. I headed down what looked like an old carriage road to see where it would take me.
Maybe a few tenths of a mile down, there was a boardwalk path that began and lead over the swamp. It was pretty cool, lots of nice views. At the end of this, the Cedar Swamp trail went right, and left would take me to Millstone Hill. I headed towards Millstone Hill, which was a nice short loop up a hill with some nice granite outcrops. I backtracked to the swamp, returned over the boardwalk and took some really awesome pictures of the sky reflected in the swamp on the way back to the car.