Being a tourist usually means a lot of walking around and eating strange food in various environments, so it would be wise to use the toilet whenever the chance presents itself. After all, in a strange city you never know when and where the next ladies room will show up...

One day you might need to ask the location of a toilet in Chinese. Better start preparing yourself for that moment right now: Qĭng wèn, cèsuŏ zài năr? = "Excuse me, where is the toilet?"

Qĭng wèn can be translated as "could you please tell..." or "excuse me..." It is the proper way to begin any question in order to make a good impression right from the start. Cèsuŏ stands for "toilet" and zài năr is "where."

If you wish to have more variety in your vocabulary, wèishēngjiān carries the meaning of ”ladies room, men's room, washroom." Literally speaking, it means "hygiene room." You can also use the term "hand wash room," xĭshŏujiān.

Worth knowing: In China toilet paper, shŏuzhǐ, might not come compliments of the house, so you'd better be self-sufficient!
Also, a Chinese toilet very often comes "opening in the ground" -style, which sets some additional requirements for clothing and physique.

International symbols are used commonly in China to indicate ladies rooms and the men's rooms, but it won't harm you to know the difference between these two characters:

男 nán = man
女 nǚ = woman

请 问, 厕 所 在 哪 儿？ Qĭng wèn, cèsuŏ zài năr? - Excuse me, where is the toilet?
卫 生 间 wèishēngjiān – washing room, toilet
洗 手 间 xĭshŏujiān – washing room
手 纸 shŏuzhǐ – toilet paper
男 厕 (所) nán cè(suŏ) – men's room
女 厕(所) nǚ cè(suŏ) – ladies room
肥 皂 féizào – soap