Oliver's comment above (SA OC 90:9 states one should make the effort to pray in a synagogue [with a minyan] than to pray with a minyan not in a synagogue) is already the answer.
Beyond that, here is how R Eliezer Melamed (RY Har Bracha) defines the obligation to pray in a synagogue (in Peninei Halakha - Laws of Prayer - chapter 3.1), see particularly in bold
When a person prays in a synagogue with a congregation, his prayer is
heard (see Berachot 6a). Even someone who missed praying in a minyan
has a mitzvah to pray in the synagogue, since it is a permanent and
special place of holiness in where prayer is more accepted (Shulchan
However, when the minyan is held in a different place, it is
preferable to pray with the minyan rather than individually in the
synagogue. If there is a small minyan in the synagogue and a larger
minyan elsewhere, although there is merit to praying in the company of
many, the value of praying in a synagogue is greater (Pri Megadim;
Mishnah Berurah 90:27-28).
Every community has an obligation to fulfill the mitzvah of building a
synagogue which will be their mini-sanctuary (mikdash me’at) and where
people can pray in a minyan. As it is written (Ezekiel 11:16), “I have
been for them a small sanctuary,” and Rabbi Yitzchak interpreted,
“These are synagogues and study halls” (Megillah 29a).
Reish Lakish says whoever has a synagogue in his city and does not
pray there is called a bad neighbor. Moreover, he brings exile upon
himself and his descendants. Those who arrive early to synagogue to
recite Shacharit and are late to leave after praying Ma’ariv merit
long life (Berachot 8a; Shulchan Aruch 90:11).
It is a mitzvah to run to synagogue just as it is a mitzvah to run to
perform every mitzvah, in order to express one’s passion for matters
of sanctity, as it says (Hosea 6:3), “We will race on in order to know
Hashem.” Likewise, when one leaves the synagogue, he should walk
slowly, so that he not appear happy to leave the synagogue (Shulchan
PS. On the definition of a synagogue, I think most people would understood as a fixed place of assembly for prayer where a sefer Torah resides in permanence. Not sure the definition matters so much although I have seen fixed places of assembly without sefer Torah (for instance, for a place used only for mincha/maariv)