Houston is one of those towns whose charms are not immediately obvious. There’s no duck tour rumbling through downtown, no crowded cluster of national monuments, no checklist of must-see buildings featured in grade school textbooks nationwide.

The Bayou City makes you look a little closer and think a little harder before she gives up her secrets.

For those willing to take the time, though, free audio tours available online can point out Houston’s quirky history and hidden gems to anyone with an mp3 player. Whether you’re part of the constant stream of newcomers drawn here for work, or a lifelong resident who’s never thought to play tourist in your own town, a guided stroll through downtown, the Museum District or Hermann Park is bound to expose you to corners of city you never knew were there.

I no doubt looked suspicious as I clutched a crudely printed map and frantically snapped photos just inside the gate of Christ Church Cathedral earlier this week while the sun threatened to set behind me.

Nonetheless, a minister gave me a friendly wave, and when I explained what I was doing he showed me around the sanctuary. Dwarfed by the office towers that surround it, the church’s size is easy to underestimate from the outside. But within, the cathedral offers an impressive display of old-world artistry in towering stained glass and ornately carved wood — not the image that springs to the minds of most newcomers when they think of Houston. The courtyard next door holds a Treebeard’s restaurant open for lunch inside a former cloister.

It’s one of those places I imagine all Houstonians hear about eventually, but it was a charming surprise as part of the audio guide to downtown narrated by Dan Workman, owner of the famous SugarHill Studios.

His sassy narrative starts at Discovery Green and wends past some of the city’s oldest houses, biggest skyscrapers and funkiest public art — with a few interesting bars along the way. Likewise, retired Channel 13 news anchor Shara Fryer intersperses her tour of the Museum District with the voices of museum curators and a Holocaust survivor.

For a shorter walk, there’s an audio guide to Discovery Green. You also can use your cell phone as a guide to each piece of sculptor Bernar Venet’s new installation at Hermann Park or download any number of podcasts produced by the Houston Zoo.

I admit that wandering around town and looking at stuff with headphones won’t appeal to everyone. But for the curious, it’s an interesting, easy and free way to enjoy a sunny afternoon.