Recently, I learned about a relatively simple way to have a raised garden that combines recycling and composting and can be a boon to folks during summer droughts or those who live in arid climates since it requires less water! From what I have read, they first appeared in Africa in areas with very little water and rather infertile soil. Villagers used whatever materials they had access to, and the idea for this sustainable gardening style was born.
Since early in September, I have been collecting used bricks with the intent of re-purposing them into a 6' diameter keyhole garden in my backyard. Based on an idea from fellow herbalist, Shelly Moore, I intend to create a separate keyhole garden for each body system, and plant the corresponding medicinal herbal allies accordingly. Shelly has done this in her yard, and I totally loved the idea because it is not only a great way to add to my teaching gardens, it also reinforces to my students that many medicinal botanicals can be beneficial to several organs or body systems at the same time - so it can help when creating a client-specific triune formula.
Here is a link to HGTV's description of keyhole gardens:
Here is one 'blueprint' for a basic 6' diameter keyhole garden: