I remember the old bear pits at Melbourne - concrete walls, concrete floor and each with a concrete "igloo", for want of a better term, to climb on. Except for the polar bear - instead of an igloo he had a (concrete) pool. No logs or anything organic in the enclosures.
Taronga's (and Adelaide's) were much the same, except that Taronga's were much deeper, being built on a steep slope.
Way back in 1970 I spent about 30 minutes watching a polar bear at Taronga playing in its pool with a small pebble. (In those days animals such as these were not given toys.) The bear was using its mouth to put the pebble on the back of its paw, then flinging it into the water and diving for it. This was not stereotypical behaviour, and he seemed to enjoy it very much. He was one of two male polars that Taronga had at that time. One died in 1984 and the other was sent to New Zealand. They were Taronga's last polars.