This is a guest entry by Trainer Flitzer09, member of the Dortmund Pokémon GO Community. This was translated into English by Tackleman.
This article focusses on useful informations about the event in Dortmund, the city of Dortmund and also some thoughts on the event.
We expect that like all the various Safari Zone events that have been taken place last year, we will see an increased number of spawns for Unown (most likely "D-O-R-T-M-U-N"), regional Pokémon from Asia and America (going back to an official article by the city of Dortmund, stating that "Pokémon usually only found in Asia and America" will be in Dortmund), as well as starters, Chansey and Larvitar.
We also think that there will be an increased chance of shinies, since that seemed to be the case at the other previous Safari Zones.
Maybe there will also be spawns of Snorlax, Bagon, Beldum, Dratini and others.
The Westfalen Park
The Westfalenpark is relatively large, however the density of Pokéstops is not that great. We think (we hope) that there will be a lot of additional sponsored Pokéstops for the event. There's also a high chance of the gyms being deactivated for the day for safety reasons, to prevent people standing in one spot. Gyms were deactivated during the Safari Zone in Oberhausen to guarantee a smooth gameplay without lag, since gym battles and raids would've caused issues.
There will be special Pokéstops like the ones in Oberhausen and other Safari Zones, that will guide people towards the park. Source FAQ.
We don't know yet if those are just there for guidance or if there will be a QR scanner within those Pokéstops to get into the actual event.
The event is definitely free for everyone and there are no tickets required! However that doesn't mean that there won't be a personal check-in at the several park entrances, where people get their QR code to check in. This feature was introduced during last year's GO Fest and the Safari Zones in Europe to prevent spoofers from enjoying the event and also to prevent huge crowds going into the shopping malls without a ticket. Safari Zone in Yokohama on the other hand was free for everyone.
The city of Dortmund is well known for organizing large events, especially around the Westfalenpark. At previous events the Westfalenpark was opened for up to 55,000 People. There are 7 large entrances, that ensure a smooth entering of the park.
There is free WiFi already and according to Niantic and the city of Dortmund, the existing WiFi will be improved for the event. Due to the large area of the park, players can easily spread out which should avoid any performance issues with the WiFi.
Since the event is free, we expect there to be around 100,000 visitors for the event.
For those who are worried that the provided WiFi might fail them, there are a few other options.
DOKOM21 is providing a lot of hotspots, throughout the city of Dortmund. Those hotspots are free for 60 minutes, additional minutes will cost extra.
Deutsche Telekom is offering a free 2-month-trial. So for those who traven internationally, it might be worth checking out. Also Deutsche Telekom usually has the best and stable network in Dortmund, according to the community.
Vodafone will also provide 20 additional COWs (celltowers on wheels).
West of the Westfalenpark (1) there are also the Westfalenstadion and the Westfalenhalle (2). Apart from the Westfalenpark, there are other parks with a high density of Pokéstops and cluster spawns around the city. There is the Westpark (3), Phönixsee (4), Rombergpark (5), Hoeschpark (6) Revierpark Wischlingen (7), Freizeitpark Fredenbaum (8) and the entire inner city of Dortmund (9).