Mobile web navigation requires highly-focused visual attention, which poses problems when it is inconvenient or distracting to continuously look at the screen (e.g., while walking). Aural interfaces support more eyes-free experiences, as users can primarily listen to the content and occasionally look at the device. Yet, designing aural information architectures remains a challenge. Specifically, back navigation is inefficient in the aural setting, as it forces users to listen to each previous page to retrieve the desired content. This paper introduces topic- and list-based back: two navigation strategies to enhance aural browsing. Both are manifest in Green-Savers Mobile (GSM), an aural mobile site. A study (N=29) compared both solutions to traditional back mechanisms. Our findings indicate that topic- and list-based back enable faster access to previous pages, improve the navigation experience and reduce perceived cognitive load. The proposed designs apply to a wide range of content-intensive, ubiquitous web systems.