The vast majority of people who come to Leavenworth do so by automobile. That works for many, but it also creates a congested tangle in the town, and makes it difficult to find a place to park. This is, after all, a small Washington town not a huge shopping center or downtown urban area. Furthermore, during many of the big festivals, it is pretty much required that some of the streets be closed off because there are simply too many people in the town for the sidewalks to hold everyone.
Thus, alternative transportation may be desirable by some.
There is a once a day Amtrak train that leaves Seattle in the afternoons and passes through Leavenworth in the early evening. Coming back the other direction, it passes through Leavenworth in the early morning. The train station is just slightly north of the main downtown area.
Transit service is offered in the area by LinkTransit, which operates a local bus service in Leavenworth as well as connecting services from Leavenworth to Wenatchee and various other communities. During the big festivals here, you may find that lodging is quite a bit less expensive in Wenatchee, and thus driving there, spending the night there, and taking the bus to Leavenworth is an advantage as you won't have to deal with the traffic and parking tangle in Leavenworth once you arrive there.
For $49.00 you can easily catch a motorcoach up to Leavenworth from Seattle Pier 69. This is a terrific option especially if you are an inexperience driver in winter weather. The ride up to Leavenworth is 3 hours one way - so 6 hours total travel time. But the time goes by quickly with breakfast of bagel w/ cream cheese; yogurt; breakfast bar; fruit; oj; and water - and the entertaining comments from the guide and driver. The only downside - transportation is only offered every other weekend and you must leave Leavenworth immediately after the town is lit up. This doesn't give you much time to enjoy the lights.
If you are planning to go to Leavenworth, it is better to drive your own car. If you don't have any, then rent a car. Transportation getting to Leavenworth is difficult. They have bus tours and train tours but these only take place during festivals like during the Christmas season. Driving a car is nice because you can stop anytime you want - stop by a the river bank for a quick walk or stop by a road corner to take some pictures.
You will most likely be driving to Leavenworth. Since the town is located in the Cascade Mountains, this can potentially be hazardous in the winter due to snow and ice on mountain pass roads. Sometimes the mountain passes around here are closed due to big snowstorms, or even due to flooding if there's too much rain. At other times they're open, but chains are required on your tires - they have checkpoints up there to make sure you've got them (if you don't they'll send you back).
If you're coming from the Seattle area, you have two choices:
1) drive north on I-5 to Highway 2 and go over Stevens Pass.
2) drive east on 1-90 over Snoqualmie Pass to the town of Cle Elum, then go north on Highway 97 over Blewett Pass.
Either way, you can check the Dept. of Transportation website below for weather predictions and pass conditions. I prefer option 2, because Highway 2 has such heavy traffic for just a two-lane road.
The best (and quite possibly the only) way to get to Leavenworth is to drive. We took our trusty Dodge Minivan. Be aware that Leavenworth is located about a 2 hour drive away from Seattle, but the road to the town is very mountainous as you pass through the Cascade mountain range. While scenic, the weather in high altitudes can change without warning.