There are two ways to get to the island of Käringön, well, actually three if you would include going here by your own boat. For all others the most likely alternative would be by taking the ferry to the island.
The ferry departs from the little village of Hälleviksstrand around 5 to 10 times a day. During the weekends the ferry only departs 5 times a day, so it might be wise to know the time tables before you go here. When missing one ferry you can easily need to wait 2 hours for the next to depart! (and I know that from my own experience). The ferry takes around 30 minutes and it is a beautiful trip; the ferry trip alone would make a trip to Käringön worthwhile to do! You can find the timetable on the website of Västtrafik. This is the current time-table
Allow yourself some time to get from the car park to the ferry, as this about a 500 metres walk. There are busses to and from Hällevikkstrand connecting with the ferry times, info on these is also available on the website of Västtrafik. If you are staying in one of the neighbouring villages like Stocken, a great idea is to just go here by bicycle, which is my preferred way to get here. Just leave your bike somewhere close to the ferry area and hop on the boat.
The alternative way to get to and from the island is by taking the boattaxi: "Käringöns sjötaxi"
Käringön (island) is even smaller than the one of Gullholmen (and Hörmanö) and also here, cars are not allowed on the island. The only mode of transport is the ferry (or private boats, albeit much more expensive). The ferry leaves from the tiny village of Hälleviksstrand and a ride takes approx. 30 minutes. The ride is exceptional though, because it leads along small rocky islands, some with tiny lighthouses, and a lot of birds accompany the boats. Ferry schedule depends on the season, in summer (2009) it was approx. every two hours, but the actual (October 2009) ferry schedule on the English website of Käringön lists fewer departures.
One-way fare was 58 SEK for adults, 49 SEK for kids in summer 2009.
Once you get to the island you only mode of transportations is quite simple: your own two feet. There is no motorised traffic on the island and I didn't even see a bicycle around. So it is walking that will bring you to the place you want. Not that the distances are that huge (remember, the island is very small!) but still, everything you bring you need to carry yourself with your own two feet as mode of transportation. So you better think twice before bringing too much ;-)
The only alternative to make life a bit easier are these little carts on the photo (don't know what they are called in English, so if you know, I would be grateful to learn what it is). A whole bunch of them was waiting at the pier waiting patiently for their rightful owners to return to the island with their luggage.