Take the famous Alishan Forest Railway narrow-gauge train from Chiayi station (the old one, not the new HSR station at Taibao). A one-way costs NTD$399 (about US$13) and takes around 3.5 hours (currently NT$240 to Fenchihu). The train passes through the scenic village of Fenchihu (奮起湖) halfway up and the village of Ruili (瑞里) is also accessible (several km away) from Jiaoliping (交力坪) station. Don't miss this trip, especially if you're a train or architecture buff, as the line is largely the same as it was before WW2 — but you might want to consider a bus for the way back (it takes about 4.5 hours for the return trip).
As of 2014, there is a daily departure from Chiayi at 9 AM, returning from Fenchihu at 2 PM. On Saturdays there is an additional departure from Chiayi at 2 PM, and on Sundays a departure from Fenchihu at 12.30 PM. Note that trains can be sold out for days in advance, if so you might be better off trying your luck coming downhill (get the bus up to Fenchihu).
During peak periods like summer and the cherry blossom season trains can get very crowded, so book ahead by calling operator Hungtu Alishan at (05)225-1978, preferably in Chinese, and show up at least 30 min before departure to collect your tickets.
Alternatively, there are sometimes "scalpers" standing outside the ticket window selling tickets at-cost, in the hope that you will also book a room in the hotel they work for or if seats are sold out on the train, they still sell standing only tickets (managed to get midweek in cherry blossom season 20 minutes before leaving) and if you're lucky you will get a seat anyway.
In Chiayi station, note that the Alishan ticket counter is on the outside of the building, separate from the ordinary TRA counters.
By bus
Very comfortable buses from Chiayi to Alishan leave roughly hourly, take just over two hours and cost NT$221 each way. However, the route isn'tquite as scenic, with more tea plantations and small villages than cliffs and mountains.
The bus ride can also be quite windy, so be careful if you have motion sickness.Buses stop at Ruili on the way. Note: The last bus to Alishan from Chaiyi is at 2PM. After that the only way to get to Alishan is by taxi which will cost $1600NT.
There is daily bus from sun moon lake to alishan. time: 8am and 9am, cost: 350NTD. it takes 3.5 hours
The last bus back to Chiayi leaves at 17:10. Buses leave from the 7-11 store across from the tourist information center. Tickets are also purchased inside the 7-11.
Note: Most take bus from Chiayi rail station to Alishan. As of Oct 2011, there is a direct bus service from Chiayi HSR station to Alishan. Only two buses a day, between 10 am to 1130am. Go to the visitors information counter at Chiayi HSR station for more info. Cost is less than NT$300 one way, takes about 2.5 hrs. If you get the driver who drives like a Daytona driver (by the name of Mr Luo), get ready the motion sickness pills and the journey is about 2 hrs including the toilet breaks.
