Offer a variety of perches. A platform perch is always a good option to include. Offer natural wood perches of different diameters to give your bird different perching opportunities; the natural variations in diameter found in natural branches will also help exercise the feet.
Huts, tunnels and similar are far too much like a nesting site. This can cause a bird to become (more) hormonal: they will probably become territorial and guard their nest fiercely, and females may lay eggs. Laying eggs can result in problems like calcium deficiency and egg binding. It's something we try to avoid as the potential risks to their health are so severe.