Enrico,
If you are competent at using Photoshop then I recommend the following:
1- Start with equally high resolution images of yourself and of the Eiffel Tower
2- Open the photo of you in Ps and "Select" yourself (use the "Refine Edge" capability in the Options Bar as needed to ensure you have a clean edge around yourself) and choose the option to make yourself a selection in that dialog box.
3- Open the photo of the Eiffel Tower in Ps. You will now have two files open simultaneously. (You could just open them both at the same time if you prefer - whatever works best with the monitor 'real estate' you have to work with and your personal working style...).
4- Reactivate the image with the selection of you again by clicking on it. Choose the "Move" tool in the toolbar. Click that on the selected image of you and drag that to overlay on the image of the Eiffel Tower.
5- Use the "Transform - Scale" function (under the "Edit" menu, to scale yourself to the appropriate size to fit the background image you've dragged it onto.
6- Use appropriate Layers Adjustments (Exposure, Brightness, Levels, Curves, Hue/Saturation, etc. - potentially with "Masking" selected parts of the image) to ensure that the lighting and color tones of the two piece parts you've combined match (or else it'll just look as though you cut out the image of you and pasted it on a background. You may want to slightly blur or desaturate 1-2 px of the edges of the image of you (just a hint) to soften the possibility of that cutout look against the Tower background. Then season the whole thing to taste (brightness, contrast, vibrance, day to night conversion...).
If you own any Ps plugins - like Topaz Remask or alternatives - you could just mask out the background of whatever's in the shot you use of yourself (it's just another, simpler, way to get a pic of you on a transparent layer) and then place the background shot of the Eiffel Tower behind/below that and reposition it as needed.
However, if you aren't real handy at Ps, then it may be easier to sell your Ps for an airplane ticket, go to Paris, and get a shot of yourself there! (I'm not kidding). :)
Good luck (I mean bonne chance)! Look up some YouTube tutorials on compositing images. Have fun. Au revoir...