The back of our house is completely flat and opens to a large rectangle yard facing a lake and some woods beyond it. We would love to add something back there to make it both more accessible and less boring, but we really have no idea what to put there.

Currently there is a single slinging glass door in the dead center of the house that opens to the backyard, with only a small 3x3 concrete block right outside the door. The patio would naturally be out there.

I know that isn't a ton of detail, but any help would be nice. Even links to ideas or pictures would be helpful. Looking online I seem to find only a ton of ideas for patios on the corners of houses rather than in the middle of a flat house.

Thanks all!!

In the meantime, here is a link with lots of photos of designer patios. Look at them less as a blueprint than with an eye toward what appeals to you:
Do you like a simple symmetrical shape or irregular?
What materials do you like?
Do you like them raised or level with the ground?
Will you be planting around it and if so, generally what types of plantings appeal to you?
Do you like structures such as walls or trellises, or do you want it more open?
What do you need room for: a couple of chairs, a large dining table, a fire pit of some kind, etc?

Are you planning yours as a DIY and if so, how much experience do you have, and how much work do you want to take on? For instance, what looks flat may not in fact actually be flat and so may require some evaluation and leveling as well as being sure that precipitation will move away from the house and not toward it.

A zone or general area where you live will help also, since some choices will depend on whether or not you need to worry about freezing temperatures, snow removal, huge amounts of rain, etc.