Lee's imaginative railway sleepers
Retaining sleeper walls...DD: Before and after pix of creative outdoor living ideas many for small spaces.
Tranquil Earth - Building Gardens with Railway Sleepers
Bench, steps & raised bed made of railway sleepers. Fairly plain layout but useful for ideas. Might need anti-slip coating for wet-weather. Like the bench to the right (mostly out of picture).
Curved timber retaining wall with vertical railway sleepers, great against a lawn. Very low maintenance
How to build a retaining wall with railway sleepers?
Sleeper retaining walls and pavior capped steps
Steps and planters in retaining wall