The weather in winter wasn't that bad - Oslo was warmer than Warsaw at that time (-5 degrees vs -25 ;)).
And now some remarks for the future (or the will-be-going-to-Oslo tourists)
- don't bother believing in the anonymous reviews of the hotels. Oslo Budget Hotel had good reviews... and was really disappointing.
- take with yourself more cash, don't believe you will get away with just having a card.
- Maestro Card is the last card (maybe except American Express) which should be used in Norway. Better take Visa with you.
- roaming is a must. I thought I would be okay with just net on smarthphone... but I wasn't.
- Oslo Pass - is very handy. You get for example: free entrance to museums, free transport. If you buy 3-day Oslo Pass you also get free ride on the ferry. Even tho we were using it for 2 days only, the 3-day Pass we bought still payed off (we rode the ferry). But next time I will probably get Oslo Package - 4-day Oslo Pass with hotel reservation.
- Get the local Oslo guides. The most important info there, imho, was the info which shops (especially groceries) are open on Sunday and longer than 17:00. I was really shocked to see that not even all the shops in the Central Station were open on Sunday.
- definitely - 2 pair of shoes needed. The Folk Museum was heavy with snow.
- ferry ride requires you to wear warm clothes. The best would be ski clothes, if you have any.
- Folk Museum is worth a all-day trip.
- Holmenkollen / Frogerseteren trip should be also an all-day trip.
- Based on my own experience - Norwegian really speak English well. BUT...! Information on coming trains is in BNorwegian only, description of food products is Norwegian only... and generally most of the written information is in Norwegian only.
I really recommend going for a trip to Oslo. I hope I will go there once more. Maybe next year.