7 - 9 hours
Leave Reykjavik and head to the town of Stykkishólmur where you can eat lunch and enjoy a boat tour around the Borgarfjord. Halfway you can stop at Eldborg Volcanic Caldera and Gerduberg Basalt Columns.
After Stikkisholmur continue to famous Kirkufell Mountain with its surrounding waterfalls. Optionally join a tour for whalewatching in Grundarfjordur and continue circling Snaefelsnes volcano. Walk up the crater Saxhóll.
Join a Vatnshellir Cave tour. On your own on the way discover plenty more stops like Arnarstapi.