Want to learn about green roof technology and how it can help the environment? The 45,000-square-foot PECO green roof features an observation deck and stunning views of downtown Philadelphia. Tours offered on the third Tuesday of each month, April through October. 25 people per tour. Attendees must be 18 years or older, and reservations must be made two business days in advance. $5 for PHS members, $10 for non-members. For more information and to register, visit pennhort.net/peco or phsonline.org/events/peco-green-roof-tour, or call 215-988-1698.