"The only place to go is down." That's what the congregation of Boston's Trinity Church decided. The landmark building, built in 1877, needed a new heating and ventilation system. Surrounded by public squares and huge high-rises (including the famed John Hancock Tower), the church has no backyard where builders could hide the unsightly equipment. After investigating a variety of technologies, the historic congregation-which has been meeting in various buildings since about 1735-decided to go with a geothermal heat pump (GHP).