Violinist Hilary Castle's concerts have become almost a springtime ritual. This Stonington native has returned numerous times to perform a show benefitting the Denison Pequotsepos Nature Center's environmental programming. The latest is today, at 2 p.m. at Union Baptist Church in Mystic. Castle is a part of Tertulia, a chamber music series in New York City, and of Project 60/40, a group of musicians who experiment with unique instrumentation. She will bring some musician friends with her for today's concert. Tickets are $20 for members, $25 non-members, and $5 students. Call (860) 536-1216 or visit dpnc.org.