4．Circumnavigating（环球航行） the planet and stopping off wherever you fancy is the ultimate trip-perfect for travellers who want to see it all，or who are just plain indecisive．But booking a round-the-world （RTW） trip can be a complex business．Here is a guide that helps to get you started．
How to do it
To buy a RTW air ticket that uses one airline alliance（联盟）can save you a lot of money．Theoretically，any routing is possible，but knowing how the RTW booking system works will make your trip cheaper．For example，the Star Alliance，a coalition（联合） of 27airlines which fly to 1，185airports in 185countries，offers a RTW ticket with a maximum of 15stops．
There are rules：you must follow one global direction （east or west-no backtracking）； you must start and finish in the same country； and it will be better if you book all of your flights before departure（出发），though you can change them later （which may cause extra charges）．
When to go
The weather will never be ideal in all of your stops．So，focus on what you want to do most and research conditions there．If a Himalaya trek is your highlight，do not land in Nepal mid-monsoon season； if you want to swim with whale sharks off the coast of Western Australia，be there between April and July．Then accept you will be in some regions at the"wrong"time-though this might offer unexpected benefits （for example，Zambia in wet season means lush landscapes and cheaper prices）．
In general，city sightseeing can be done all the year round （escape extreme heat/cold/rain in museums and cafes） but outdoor adventures are more reliant on-and enjoyable in-the right weather．
Where to go
The classic （and cheapest） RTW tickets flit between a few big cities，for example London-Bangkok-Singapore-Sydney-LA．If you want to link more offbeat（标新立异的） hubs （Baku-Kinshasa-Paramaribo，anyone？），prices will climb considerably．The cost of the ticket is based on the total distance covered or the number of countries visited．
Remember，you do not have to fly between each point：in Australia you could land in Perth，travel overland and fly out of Cairns．Or fly into Moscow，board the Trans-Siberian train and fly onwards from Beijing．
Pick some personal highlights and string the rest of your route around those．For instance，if you are a keen trekker，flesh out a Peru （Inca Trail），New Zealand （Milford Track） and Nepal （Everest Base Camp） route with Brazil （Rio's a good access point for South America），Australia and northern India．
If budget is an issue，spend more time in less expensive countries．Your daily outgoings will be far higher in Europe and North America than in South-East Asia．Indonesia，Bolivia and India are particularly cheap．
Pay attention：
Talk to an expert before you book：you may have a route in mind but an experienced RTW flight booker will know which routings work best and cost least-a few tweaks could mean big savings．
Be flexible：moving your departure date by a few days can save money； mid-week flights are generally cheaper，as are flights on Christmas Day．
Think about internal travel：it can be cheaper to book internal flights at the same time as booking your RTW ticket．But，with the global increase of low-cost airlines，you may find it better （and more flexible） to buy them separately as you go．
Be warned：if you do not board one of your booked flights （say，on a whim，you decide to travel overland from Bangkok to Singapore rather than fly it） your airline is likely to cancel all subsequent（后来的） flights．
A （71）Guide to a Round-the-World Trip
| How to do it | •To buy a RTW air ticket （72）usingone airline alliance is a most economical way．
•To follow one global direction and start and finish in the same country；
•To book all flights before you （73）depart/leave． |
| When to go | •To arrive at your destination at the right time，（74）researchweather conditions in advance．
•To be in some regions at the‘wrong'time offers benefits beyond （75）expectation（s）．
•Generally，city sightseeing can be done all the year round，but outdoor （76）adventures are more enjoyable in the right weather． |
| Where to go | •Cheap cities like London and Sydney．
•Unusual places like Baku （77）costingmuch more．
•Less expensive places in consideration of（78）budget． |
| （79）Tips/Suggestions/Adviceand warnings | •Turning to an expert before you book．
•Being flexible about your departure date．
•（80）Failing/Failure to board one of your booked flights may lead to the cancel of all subsequent flights． |
