The incredible bassriff comes in at 4.40. It's very easy:
G--------------------------------------------------|
D--5-5-5-5-7-7-9-9-10-10-10-10-12-12-12-10-9-9-9-9-|
A--------------------------------------------------|
E--------------------------------------------------|
G--------------------------------------------------|
D--10-10-9-9-7-7-7-7-9-9-9-7-----------------------|
A--------------------------------------------------|
E--------------------------------------------------|
You just keep repeating this part until 6.08. Then you just keep on doing...
[ Tab from: https://www.guitartabs.cc/tabs/s/sigur_ros/festival_btab.html ]
G--------------------------------------------------|
D-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5-5--|
A--------------------------------------------------|
E--------------------------------------------------|
...until 7.33 when there's a little fill:
G--------------------------------------------------|
D-5/12-12-12-10------------------------------------|
A--------------------------------------------------|
E--------------------------------------------------|
Then just keep on repeating the first riff for the rest of the song.
Enjoy and buy the record! It's great!
