Just as the Achievement states, Win a match/event in 50% of the games venues. Not all venues are accessible from the start. You will have to play World Tour to either play in all the venues*, or if you want them for quick match also; You will have to win certain events for a certain medal.
In total you have 36 Venues to win in and 29 that you have access to from the Hit The Streets mode (Not including Custom Matches**). Here is a list of the venues for which game type you can play in for Hit The Streets (so some may overlap). I also put down what event and criteria is needed to unlock certain venues.
Venues:
Last Man Standing:
- Basket Ball Court
- Shanghai Rooftop
- Aberdeen Cage
Futsal:
- Futsal Centre
- The Hanger
- Placa De Catalunya - (Adidas World Futsal Championship - Stage 4 - Gold)
- Tokyo Futsal Stadium - (Tokyo Futsal Shield - Stage 4 - Silver)
- Rio Stadium (Daytime) - (Adidas World Futsal Championship - Stage 4 - Silver)
- Rio Stadium (Night) - (Adidas World Futsal Championship - Stage 4 - Silver)
- Berlin Stadium - (Berlin Futsal Tournament - Stage 3 - Bronze)
Panna:
- Aberdeen Cage
- Basketball Court
- Empty Parking Lot
- Loading Bay
- Shanghai Rooftop
- Buenos Aires - (Bueno Aires Panna - Stage 4 - Silver)
- Skate Park - (Freestylin' Dublin - Stage 3 - Bronze)
5 A Side:
- Underpass 2
- Goals Centre (Daytime)
- Goals Centre (Night)
- The Dome
- Indoor Court
- Justin Chan Memorial
- Adidas Z5
- London (Evening) - (London European Championship - Stage 3 - Bronze)
- London (Daytime) - (London European Championship - Stage 3 - Bronze)
- New York Stadium - (New York 6 Tournament - Stage 4 - Silver)
- Dubai - (Dubai 5 A Side Cup - Stage 4 - Silver)
- Paris Notre Dame - (Notre Dame 5 A Side Tournament - Stage 3 - Bronze)
- Venice Canal - (Venice 5 A Side Event - Stage 3 - Bronze)
- Barcelona Stadium - (Freestylin' Barcelona Tournament - Stage 3 - Bronze)
- Amsterdam Stadium - (Amsterdam Panna Tournament - Stage 4 - Silver)
Primary Note - You should play 95% of the maps during world tour. Some maps can only be played by making a Custom Match in Hit The Streets. You will need to make a Freestyle game, with a goalie, 2 players to be able to play in the Gym, and Football Complex. You will have to make a 5 man team with the same settings to play Indoor Court.
Thanks to moroniccow for bringing this up in his solution.
*After playing all the side events on Stage 3 (Europe for me) and beating one of the tournaments (Notre Dame) I still didn't have "Sightseer" for playing on 50% of the maps. I had the feeling I hit 50% already so I checked out the venues and the issue was I skipped a map (Loading Bay) in North America, so I just did a Hit The Streets match real quickly. Once I did that the achievement unlocked.