This 27 February 2018 video says about itself:
This bird feeder is situated in one if the best birding areas in Europe – The Rose Valley in Central Bulgaria in a village yard. This is a very special place – within one year we counted 170 bird species. In the same yard we have a specialised underground bird photography hide for max. 4 photographers or bird watchers. From this hide we photographed 50 bird species.
You can see more details on our website.