What are the most worthwhile things to do in Las Vegas on a first visit?

Hoover Dam is the most consequential structure anywhere near the city, and its numbers hold up to a close look. It rises 726.4 feet from foundation rock to the crest roadway, with the towers and ornaments on the parapet adding another 40 feet. The dam itself contains about 3.25 million cubic yards of concrete; counted together with the powerplant and the appurtenant works, the total is 4.36 million cubic yards. Concrete placement ran from June 6, 1933 to May 29, 1935, and all features were completed by March 1, 1936. Around 21,000 men were employed over the course of the project.

Red Rock Canyon, on the far side of the valley, is the landscape counterweight, and it is rationed. Reservations open on a rolling daily basis at 7 a.m. Pacific time, up to 30 days ahead, with a second release two days out. Between those two release points, a trip planned a week out is not locked out — but it does depend on catching the 7 a.m. opening on the right morning.

Lake Mead National Recreation Area completes the set. The lake is the reservoir the dam impounds, which makes a day taking in both the structure and the water a single coherent story rather than two separate excursions, and the recreation area charges its own entrance fee by vehicle, motorcycle or person, with an annual pass available.

At the dam the canyon walls close in tight enough that the structure fills the view from the approach road, and the drop below the downstream face is the part photographs rarely convey. The concrete is pale against dark volcanic rock, a contrast that holds at every hour of the day.

The concrete-placement window is much shorter than the dam's reputation suggests. The pours ran from June 1933 to May 1935 — under two years — with every remaining feature finished by March 1936. That compression is why the structure reads as a single design rather than an accretion of phases, and why the ornamental towers along the parapet, which add 40 feet above the crest roadway, are consistent from one end to the other.

• Set an alarm for 7 a.m. — Red Rock's reservations release at that hour, 30 days ahead and again two days ahead.
• Dam in the morning — East of the city, the approach and the downstream face read best before the day's heat builds.
• City after dark — The built environment is the one part of a Las Vegas visit that genuinely improves at night.

Reservations at Red Rock are released only at those two fixed moments, so a plan made 10 days out has to wait for the two-day release and may not clear it. Hoover Dam is a working federal power facility straddling a state line, so access to specific areas inside it is controlled and can change on short notice. Summer temperatures in the valley make midday activity at either site a serious proposition rather than a casual one, and neither offers much shade. Federal annual and lifetime passes substitute for the Red Rock entrance fee but not for the timed-entry reservation itself — those are two separate requirements.

The Las Vegas when-to-visit question in this group gives the monthly temperature normals that determine which of these two sites is comfortable in your travel month.