In both seasons of Sound! Euphonium we see Yamashiro Sports Park (also known as Taiyogaoka). The closest train station is Shinden Station, but I walked here from Uji.
Image from S1E5 - 14m24s
This is where the SunFes in episode 5 of the first season is held.
Image from S1E5 - 18m44s
Closer look at the field.
Image from S1E5 - 14m26s
There was some kind of event going on when I was here, so I couldn't get too many pictures.
Image from S1E5 - 14m56s
The gates behind Matsumoto and Taki matches. I only got a picture from a different angle compared to the show though.
Image from S2E2 - 03m29s
Image from S2E2 - 03m31s
In the sports park there's also the pool they visit in episode 2 of the second season.
Image from S2E2 - 03m35s
The pool area seemed to be open, but there were nobody there.
Image from S2E1 - 46m02s
So I walked in an got some quick pictures.
Image from S2E2 - 08m20s
Most of the pool area seen in the show seemed to be closed off with ropes, so I didn't get any pictures that matched that well. You can see the similar outdoor showers and covered sitting places here though.
This location was visited on 2016/10/21.
Yamashiro Sports Park official website
Special thanks to the ones who went here before: