Piedra Herrada monarch sanctuary
About 40 minutes by car. From roughly late November to March this is the standout trip and the one genuinely built into why you came: forest thick with overwintering monarch butterflies. You go with a local guide, and the climb is short, steep, and at real altitude, part of it can be done on horseback if you would rather not walk it all. Go early on a warm, clear morning so the butterflies are active and flying rather than clustered and cold. Allow half a day with the drive. Verdict: worth it in season, easily the best day out from Valle. Out of season it is just a forest walk, so skip it then.
Avándaro and Velo de Novia waterfall
Around 15 to 20 minutes. The leafy residential zone south of town, with the Velo de Novia falls a short walk from parking. Pleasant for an easy half-morning drive and a quick look at the waterfall, plus a glimpse of how the wealthy end of Valle lives. Verdict: fine as a tack-on, not a day trip in its own right. Combine it with a lazy morning rather than building a whole day around it.
Nevado de Toluca
Roughly 2 to 2.5 hours by car. The dormant volcano east of Valle, with two crater lakes (the Lagunas del Sol y de la Luna) you can reach by road much of the year, weather and park access permitting. It is high, cold, and genuinely dramatic, real high-altitude scenery for anyone who wants a proper mountain day. Verdict: worth it, but as its own full-day expedition, not a Valle add-on. The altitude and the drive eat the whole day, and it is honestly easier reached from Toluca than from Valle.
Toluca
Roughly 1.5 hours by car. The state capital, with the Cosmovitral botanical garden set in a stained-glass building and a well-known Friday market. Useful mostly as a stop en route to or from Mexico City rather than a dedicated trip out of Valle. Verdict: skip as a day trip from Valle; see it on the way through if the timing lines up.
Honest take
The monarchs are the one day trip that justifies itself, and in season they are reason enough to make the drive to Valle in the first place. Everything else is optional and, frankly, better reached from elsewhere. If you only have the two days the town warrants, spend them in and immediately around Valle rather than chasing farther-flung stops. The ruins at Teotihuacán sit on the opposite side of the state and are a separate trip out of Mexico City, not a same-day pairing with Valle. More on structuring your time is in the main Valle de Bravo guide.