Heroic Maps helps you get over those waterways and flowing lava with their new bridges maps pack.
From the release:
A printable geomorphic dungeon floorplan compatible with any RPG/Dungeon-Crawl game. Use as a standalone gameboard, or combine with any same-scale tileset.
Contents: Six 10×10 battlemaps showing various bridges crossing rivers. There is a small wooden bridge crossing a 20ft river, a small stone bridge crossing a 20ft river, and also a ruined version of the stone bridge. For creating much larger bridges, three tiles depict the two ends and middle of a large stone bridge, which can be used to make very long crossings, or combine the two ends to make a medium-sized bridge.
Uses: Take your adventurers across the bridge to new areas, watching out for jealous trolls as you cross. Defend the crossing against bandits, enemy armies and sieges, Use the bridge as a chokepoint to even the odds against an overwhelming army. The Bridges set can be combined with the rest of the Heroic Maps wilderness and countryside range to make huge outdoor environments,
Also included is a set of 300dpi full size jpgs, for poster printing or VTT, in both gridded and gridless versions. (n.b. gridless version only in jpeg format)