From a central tuft grow mats of tiny leaves on long, trailing stems ending in large, open flowers later in summer. The flowers are intense violet-blue (Cyananthus means, literally, blue flowers). Spreading mats, 5cm (2") high. Dies back for winter and reappears in spring.
A special, classy plant that likes a peaty (or humus rich) soil in a lightly shaded spot or in sun where it won't dry out. And no lime. Given those, it's an easy and rewarding plant to grow.