for most of us, the days of traditional double exposure are long gone with film. the good news is that there is also a way to achieve this effect using 2 different photos and photoshop...
1. begin with a landscape photo of your choice.
2. in photoshop, layer a second photo on top. this photo must have a bright background. to avoid the window panes like in the above photo, you can take the picture against a white wall.
3. position the second photo then begin playing with this layers blending mode. i tend to prefer 'overlay' or 'screen'.
4. to finalize, you can then adjust levels, contrast, etc. until you get the look that you want. on the image below, i even added a bit of text.
happy photographing!