I am always on the lookout for interesting things to listen to while gardening or taking a walk.
For the last few years I have participated in SYNC which is a free audiobook program for young adults, aged 13 and above. Although ostensibly the program is for young adults, age is no impediment (myself being a case in point). The titles are thematically paired each week.
In 2014 the program will be running from May 15th to August 13th, during which time you will be able to download two different complete audiobooks each week to keep.