( )=on peut omettre wich
[ ]=on ne peut pas omettre wich
The sky on the outside of the Sydney Tower [which] is now called the Eye is the scariest thing (which) I have ever done . The tower , [which] is 268 metres high, is the tallest building in Sydney . I was okay on the Harbour Bridge climb [which] is the second highest climb (which) you can do in Sydney [which] I thought was the capital of Australia until my guide told me that was Camberra [which] was the capital .
Voilà :) tu pourrais presque enlever tous les « wich » si tu modifiais les phrases. Mais si on ne les touche pas tu dois les laisser à certains endroits