Assassin's Creed: Revelations. First off, let's get the protagonist problem out of the way: In Revelations, you'll play as both 12th century stabber Altair and his 16th century descendant Ezio, now over 50 years old. Ezio will be looking for "seals" which will allow him to access Altair's memories, similar to how Desmond used the Animus to access both Altair's and Ezio's memories. Speaking of Desmond, he's unsurprisingly back in the Animus "where he finds a safe mode called the 'Black Room.'" The gameplay in Desmond's mode is described as "narrative-fueled puzzle sequences," geometric shapes and all.
The lion's share of the game will take place in Constantinople (or, as it's known today, Istanbul) separated into four districts: Constantin, Beyazid, Imperial, and Galata. If you want a change of scenery (fairy chimneys!) some of the game will also take place in Cappadocia. Inside the cities, you'll be able to establish Assassin's Dens, a sort of expanded Borgia Tower mechanic from Brotherhood. Complete various scenarios, take down the regional Templar presence, establish a Den, and then "upgrade the buildings in that region along with adding ziplines across the rooftops."