At the very northern point of the Edsviken lake is Edsbergs Slott, what appears to be a fortified manor or castle looking down the length of the lake. Some of the formal gardens are still maintained although it appears that the castle itself is no longer used as such - I didn't investigate too closely but there was no sign of it being used either as a home or a tourist attraction, more like a council office.
In the grounds, though, there is a new-ish art centre perched upon a nearby rock outcrop.
On my way back to Akalla from the Slott I found yet another part to Sollentuna, a large out-of-town style shopping centre with plenty of access and parking for cars but somewhat pedestrian unfriendly (not as bad as some examples I've found in the UK, we seem particularly good at unfriendly). The centre contains a really large food (plus home etc things, think Tesco but Swedish) shop, and a number of high street shops. Nothing spectacular on its own but combined with the other two centres of Sollentuna makes it quite a well served place, in a retail sense at least.