There are buses to Ubby (stop Djärvs vägskäl) which run just a few times on weekends. Come early and enjoy swimming in the lake and boating. Here are the options: car/car share with anyone driving is the easiest option.
Driving. If you come up the E4, turn off at Arlanda and follow 273 to Gottrora, then turn towards Rimbo. About 1.5km down the road turn off left towards Rånäs, then after 4.5km turn left towards Knutby. Follow this to the Abrahamsby turnoff, then follow hash signs.
Alternatively, E18 to Rimbo, then E77 for 6km then turn right towards Rånäs. Go past Fasternas Kyrka and the ruined castle, then left and right towards Knutby to Abrahamsby turnoff.
Cycling. It is 33km via scenic back roads from Märsta to via Vidbo/Husby and Abrahamsby. Take the train to Marsta and enjoy a ride through the countryside. See if you can break the record of 8 hours set by Sprintosaurus last year
The nearest stop is "Djärvs vägskäl", which is actually one stop past Ubby, when the bus is on its way back to Rimbo. (The bus does a loop at the end of the line)
1000 Bus 639 Tekniska Hogskolan - Rimbo, 11.02 Bus 648 Rimbo - Ubby 11.38.
Alternately 1300 Bus 639 Tekniska Hogskolan - Rimbo, 1358 and I will try to organize pickups from Rimbo to here.
Getting Home. The last local bus leaves Ubby at 1808, so you can make that if you leave right after the run. But stay over if you can, there is early bus from Rånäs, or a later bus (1136 from Ubby).
If you need to get home Saturday evening there are buses every hour from Rimbo. We will try and get people into cars (I won't be driving however...) or will arrange a late taxi pickup if we have enough people.
Hopefully the weather will be better than last year.,,
Stay over if you want, we have plenty of crash space (first come gets the stuga, also two bunks and a bed in the workshop, and unlimited floor and camping space), will put on breakfast (free) for those who stay. If you do the ride, you can ride back to Märsta in the evening or next day.
Update Wednesday 17: Having had temperatures in high 20's and dry for the last two weeks, weather is now looking iffy. Sprintosuaurus has laid bike trail from the station to here (and incidentally traumatized Little Fart when he turned up, since she recognized him and assumed the rest of the pack would be along and we would be going for a run). Starting from there at 1010, but you could start later if you take a direct route (takes about 2 hours, ask Google Maps/follow 273 as per driving instructions)
Let us know if you are coming.