The third-age druidic robe top is part of the third-age prayer set. It requires 65 Prayer and Defence to wear. It is currently the only third-age platebody-slot item to offer a prayer bonus.
A livestream with Mod Simon and James revealed the mechanics of Treasure Trail rewards in detail, meaning the actual chances could be calculated: approximately 1 in 37,128 per item roll for any of the 5 parts of third-age druidic, or approximately 1 in 185,640 for a specific part, per item roll - with an average of 5 item rewards per Trail, this gives approximately 1 in 7,426 for any part, or 1 in 37,128 for a specific part, per Trail completed. For a more detailed breakdown of drop mechanics and calculations, see Treasure Trails/Rewards#Elite.