On 18th march 2020 i was walking with a group of four friends over the old oswestry hill fort in shropshire, uk. we had stopped to take some tea and while we were getting this ready we all heard a humming and buzzing noise approach us from behind and to the north west. we turned around and literally in the sky right in front of us was this very weird looking triangle shaped 'thing's that was clearly not any aircraft inhave ever known or seen. it was moving slowly sort of towards us and quite low, i would say approx 400 to 500ft altitude. ot made a slight turn and flew from right to left in front of us heading in a southerly direction towards the town of shrewsbury. this craft was actually quite bizarre looking and made this strange hum as it flew by. i am a retired royal air force air traffic controller with 20 years service and i have never seen or known anything like this before i retired in 2019, so i am fully aware of all drone technology in the military, and can confirm that this was not anything even remotely near that! i have seen some pretty exotic aircraft in my time, and have been based at places like mod boscombe down, but this craft was unlike anything in had ever seen before!