This is another popular form of concrete blocks used to make breakwaves.
In 1985 if you wanted to be a civil engineer in France (Ingénieur TPE) you had to draw an isometric perspective and a side elevation of the block, given the plan & the front elevation (proposed here). Wanna try ?
My challenge was to make it in 3D with the same data...not that easy either!
If not scaled the print will be 40mm high.