Complex sentence: It became famous in 1990, when the Bulgarian military started works in the centre of the village, because a woman received signals from aliens that the world's first "smart" creature was buried under Tsarichina.
Split into simpler sentences: It became famous in the early 1990s, when the Bulgarian military began digs in the centre of the village. The project's aim changed because a woman received signals from aliens that the world's first "intelligent" creature was buried under Tsarichina.