Most of us can always use some lower back stretches, and this one called Butterfly Pull stretches your entire spine and opens your hips as well.

• Partner #1 (blue shirt) sits in Butterfly [1] pose with his heels together and knees out wide.
• Partner #2 (no shirt) sits with his legs straight facing Partner #1, and places his feet on Partner #1's shins.
• Both partners hold each other's hands or wrists. Partner #1 folds forward over his feet as Partner #2 leans back, pulling him deeper into the stretch.
• They hold for five or so deep breaths, making minor adjustments if necessary. Then both partners slowly sit back up and they switch roles.

Source [2]