Touhou shows up in a lot of places. Here are some places you might have been, especially if you've been on the internet for a long time. A lot of this is music.

Section 1: Non Weebs May Know

Bad Apple!!

This is an MMD animation made to a remix of Bad Apple, a song from Lotus Land Story. Honestly, we're still confused to this day why they picked a random stage song to make a banger remix of, but hey we won't complain. Almost everyone has seen this video or heard this song if they've been on the geekier side of the net. It's a great MV, including many characters from the early windows games.

UN Owen was Her + Impossible Piano

Decided to put these entries together, as they're related. UN Owen was Her is by far one of the most popular Touhou songs. We've heard somewhere that this 'impossible piano' showed up in a local news station once, but I don't have a source for that. (Might come back and try to find it.) UN Owen was Her is a great piece of music, perfectly fitting Flandre Scarlet's craziness.

References in Undertale

It's fairly well known that Toby Fox is a big Touhou fan. You can hear it in his music and feel it in his danmaku. Some of Asriel Dreemurr's attacks seem to be inspired by a few of Marisa Kirisame's. Tsunderplane is the most obvious reference, as it's an anime girl-type creature wearing a mob cap with a bow. This hat looks a lot like Yukari Yakumo's, but it's also a naturally spawning object on early windows Touhou girls in general.