Fares from SFO/SJC/LAX to Europe are higher on average this first day of May than they were one month ago, which makes $620 round trip in August from SFO to Vienna, Austria look like a good deal today.
Vienna seems to be a regularly high priced destination city in my observations of airfares the past couple years, so a round trip fare in summer close to $600 is actually a low fare on average for this city.
These tickets are $610 to $640 for travel August 14 to October 20 before prices rise to mid $800s and $900s; a more typical airfare for this route.
Flight itineraries I checked offered outbound flights on Finnair from SFO to Helsinki to Vienna. There are options for a 16-hours overnight layover 4pm to 8am or a short under 2-hours layover between Helsinki flights.
American Airlines San Francisco SFO – Helsinki HEL – Vienna VIE – London LHR – Phoenix PHX – San Francisco SFO
All returns Vienna via London LHR to SFO I saw were British Airways transatlantic flights.
Even lower $597 in Momondo searches returning to San Francisco via Dublin with Aer Lingus.
On Momondo, the price went up to $742 for routing via Helsinki in both directions.
American Airlines ticket SFO – Helsinki (overnight layover 3:50pm-8:30am) – Vienna – London LHR – San Francisco SFO