OK, thanks. Finally SEEMS to work. A lot of things left to make sense with but anyway;) To keep things together I used:

In Nodes window header chose "Type of data to take shader from" to "World".
Added nodes: texture_coordinate (generated) -> mapping (vector) (in that node, under "Vector" tab set Scale to 0.5 x 0.5 x 0.5) -> environment_texture (color) -> background -> world_output
In 'world' panel loaded the HDRI, set Surface to "Background" and Color to "Environment texture".

And got anything better than a pink sky :biggrin: