旅游: used very common 多见用于口语 vi
eg。去旅游,去(某地)旅游,从(某地)旅游回来
旅行:书面更多, vi 旅行= 旅游
eg,1.人的一生都应该经历两件事 一次说走就走的旅行 和一次奋不顾身的爱情(recently very hot used in China, People should have such two experiences in their life, one is a voyage without any hesitation when the idea occurs, the other is falling in love with sb regardless of any barriers lying in front of you )
2.她上个月去了法国旅行。
观光: 多见于书面, vi , 观光=旅游,we can also say “观光旅游/行” as one word
more often followed by another noun to form a new word that is relative to the "tourism"
eg。 观光电梯(elevator, lift), 观光农业(agriculture), 观光路线(route)
游览:vt 游览某地
eg. 他去年来中国游览了长城,故宫和颐和园。
他游览了整个北京城。
:)