The other side of the elephant house borders a raised hillock, and elephants could walk up and down. This passage has a broad metal fence and a gate, so could be blocked.
As already said, the building still stands in Warsaw Zoo as of 2020. The building is renovated inside, the gate to the roof is permanently closed, and a breeding pair of Indian rhinos lives there. The photo below shows the other side of the building, it seems the former gate to the roof is now additionally hidden behind a row of rocks. Rhinos couple - ZooChat Rhino's outdoor exhibit - ZooChat
By the way, it has been long known that elephants respects heights and will never voluntarily step down a vertical slope over ca 1.5 m high. This was the basis of many steep but narrow moats in tens of zoos. Warsaw zoo was the only one which taken the idea further, and let elephants go high up. Warsaw zoo stopped letting elephants on the roof probably in the 1960s-70s. Much later, zoo enthusiasts compiled evidence that elephants should not be kept behind steep-sided moats because they push each other down leading to injures. In Warsaw, it never happened - zoos last Indian elephant died of old age in 1998.
