Norway uses Norwegian Krone (NOK). The exchange rate fluctuates but has recently been very close to 1 EUR = 10 NOK. You will not need to withdraw cash, credit cards are accepted almost everywhere.
July in Oslo is usually warm but not hot. Maximum temperatures are usually between 20 and 30 °C while it could be 10 °C cooler at night. Average rainfall is 87mm in July, but varies a lot. Yr.no/en has a local weather forecast.
You would not go to Oslo for a beach holiday but there is actually a popular beach right next to the Oslo Opera House, the Operastranda. Expect temperatures around 20 °C.
Among the most popular sights in the city centre are the Akershus Fortress, the Oslo Opera House (where we are having our Thursday evening event), The Royal Palace, the recently relocated Munch Museum and the even more recently opened National Museum.
A Short distance by boat from the keyside in front of the City Hall to Bygdøy you will also be able to visit the Fram Museum, the Kon Tiki Museum and the Norsk Folkemuseum – Norwegian Museum of Cultural History.