noun, verbal noun
You pass through somewhere for a reason, so you're going via that place.
This is a jukugo word that uses the on'yomi readings of the kanji. You learned this reading for 経 with the kanji, and you learned this reading for 由 with the word 由来. If you need an extra reminder for that one, here's a mnemonic just in case:
If you're going via an unfamiliar place, I recommend you seek out a yurt (ゆ) to stay in. Wherever it is you're going via, you can't go wrong if you stay in a yurt.
That's the time I went to Kyoto via Tokyo.
You can also go via Osaka.
I think it's best to book your inn via the internet.