Exploring Hailes Cave. 7 p.m. at the Clarksville Community Church. Thom Engle of the Northeastern Cave Conservancy will present a program on Hailes Cave.  Of the caves known in Thacher Park, Hailes Cave is the longest.  Historically the cave was visited frequently, but in recent years it has been inaccessible.  With the new Thacher Master Plan the cave is being remapped by the Northeastern Cave Conservancy, the same group that owns Clarksville Cave.  Take a photographic and cartographic tour of the cave and learn what is there and what the future of exploration may reveal. 768-2870.