The La Moneda Palace tour is a straightforward 45-60 minute guided walk through the Chilean presidential headquarters. You'll see the main courtyard, parts of the original 18th-century architecture, ceremonial rooms, and a small but decent collection of presidential gifts and historical artifacts. Expect decent but not spectacular historical commentary - more facts than storytelling. Security is tight; you'll go through airport-style checks and can't bring large bags. The experience is interesting if you're into politics or architecture, but it's fairly formal and not especially exciting for most casual travelers.
Best time to visit is spring (September-November) or fall (March-May) when Santiago's weather is pleasant and crowds are lighter. Summer can be hot and crowded, while winter often brings rain. Expect to pay around $15-25 USD per person including the standard guided tour. Private or premium options run higher. Book ahead if you're visiting on a weekday when government functions might restrict access.
Honest tip: take the tour that includes the underground cultural center and exhibition space - it's genuinely the most interesting part for most people. Skip the basic exterior-only visit; it's not worth much. Go early in the day for the best chance of seeing the changing of the guard in the plaza afterward. If you're short on time in Santiago, this is skippable unless presidential history specifically interests you.