What's the must-see thing in Austin?

The Texas State Capitol stands 308 feet tall at the head of Congress Avenue, 15 feet higher than its federal counterpart in Washington, D.C. The exterior is sunset-red granite from a quarry near Marble Falls, about 50 miles northwest. Step inside and the rotunda floor is terrazzo, cool underfoot even in June when it's 35°C outside. The building opened in 1888 and still houses a working legislature, so you'll likely walk past staffers in the hallways. Free guided tours run every 30 to 45 minutes on weekdays starting at 8:30am. Saturday tours start at 9:30am. No reservation, no ticket. The south lawn gives you a straight sightline down Congress Avenue to the river, which is the best way to orient yourself to Austin's grid on your first morning.

Barton Springs Pool in Zilker Park is a 3-acre spring-fed swimming hole that holds at roughly 20°C year-round. In summer, when the air hits 38°C by 2pm, that water feels like jumping into a cold creek. The limestone bottom is slippery in patches and the water is slightly green from natural algae. It's not a resort pool. Lifeguards patrol, the concrete deck gets crowded on weekends by 11am, and the shallow end has enough kids that you'll want to swim toward the deeper north section for actual laps. Admission runs $5 to $9 depending on the day and whether you're a local. The pool closes Thursdays for cleaning. The 10-minute walk from the parking lot along Barton Creek Trail passes under old pecan trees that keep the path shaded even at midday.

The Lyndon Baines Johnson Library and Museum on the University of Texas campus opened in 1971 and holds 45 million pages of presidential documents. The top-floor replica of the Oval Office tends to be the crowd favorite, but the civil rights exhibits on the ground floor are the reason to go. You'll stand in front of Johnson's actual desk phone, the one he used to press legislators for the Civil Rights Act of 1964. Admission is free. The building itself is a brutalist concrete slab designed by Gordon Bunshaft. It looks like it was dropped onto the UT campus from another decade. Plan about 90 minutes. The museum sits on the east side of campus, a 15-minute walk from the Capitol.

The Congress Avenue Bridge bat colony gets attention, and between March and October roughly 1.5 million Mexican free-tailed bats emerge at dusk. For a first-time visitor with 2 or 3 days, though, it's a single 20-minute event that requires you to be at one spot at sunset. That conflicts with dinner on South Congress. If you happen to be near the bridge around 8pm in summer, stay and watch. Don't rearrange your evening for it. Start your first morning at the Capitol at 8:30am, walk south down Congress Avenue for 20 minutes, eat lunch on South Congress between Elizabeth Street and Monroe Street, then rideshare 10 minutes to Barton Springs for a 2pm swim. Save the LBJ Library for morning two. This sequence keeps you moving north-to-south with the sun at your back and puts the swim at the hottest part of the afternoon, which in June means 35°C or higher.