Based on the information about prehistoric cave art and the context you provided, the three true facts could be:
- Some stenciled images were made by blowing paint.
- Artwork is considered to be the oldest so far.
- Cave is full of full human figures.
However, specific details about the discovery mentioned (found in Austria by amateur speleologist on Dec. 18, 1994) need to be verified for accuracy. If those details are indeed true according to historical records, then it could also be selected. Please adjust based on accurate knowledge of the specific artwork in question.