Here is a selection of localities that are easy to find, in and near Oslo city centre. Start: Natonaltheateret stasjon. End: Vulkan/Kuba. I have added references, but you can also check my book (under asfalten, kagge forlag) for further details.
Localities to visit
Light greens: Ordovician (shale/carb). Bright green: Cambrian (black shale). Purple: Permian sills in shale. Light pink: Basement gneis. Dykes in red (thin lines).
First: A few nice and old maps
Norges geografiske oppmåling – lots of new data

Grotten – the arnestad Formation at 30 degrees southern hemisphere
Slottsparken – ordovician volcanism & cyclostratigraphy
Olav V gate – A hidden ordovician “svaberg”
Akershusstranda – basement horst and cambrian shale
Eruption in Holuhraun, Iceland. Taken 1st. of september 2014. The location is north of Bardarbunga volcano.
Kontraskjæret and the first pulse of permian volcanism

From W.C. Brøgger, 1882
Trefoldighetskirken (lost locality) and vestre gravlund – cambrian and ordovician
Gamle aker kirke – Huk Fm. Limestone
akersberget silver mine – metal mobilization and precipitation