You have an extraordinary possibility to see a part of Riga from an unusual view.
Just take some boat of your choice and try not to disturb other participants of the Riga Channel traffic too much. Wherigo is made as a tour guide with a short desription of particular places. You don't have to count or calculate anything, just visit all points in the correct order and your device will take you to the cache. Please take into consideration that the trip starts and ends in Andrejsala.
The Wherigo cartridge you can download here