1. The raw pic with all the tourists milling about

Note the LHS the thumbs in the layers panel. There is the base photo (called background layer) underneath and the Layer 1 on top which is invisible (the eye icon is missing). Also note the white rectangle which is the layer mask.
2. The Layer 1 photo with the tourists in different places. I've deactivated the mask (rect with red cross) and the raw pic (background layer) so you can see what the 2nd pic is like

3. With Layer 1 and its mask active as well as the raw pic. I had to do a bit of transforming on the layer so that both pics match. After this I can simply erase what I don't need much more easily

Hopefully this will give everyone some idea of photoshop layers and what you can do with double exposures in a busy area. Please note I'm no photoshop artist but still a lowly IT support guy - I just happened to learn this from searching the web.