There's nothing quite like David Rumsey Maps in Second Life. Spread out on four sims are some remarkable cartographic treats—and I really mean spread out! The gargantuan map above is one of New York City from 1836, stretched out to be 200x100 meters, allowing one to literally walk around the neighborhoods (we're standing in lower Manhattan—click to zoom in). That's the Brooklyn Bridge around the center of the photo, spanning the East River. Most of the upper part of the island seems to be farmland, large estates, and military installations. But already, running way up the West Side, is Tenth Avenue. :) If you would like to get a smooth overhead experience, sit on one of the map viewers (brightly colored arrows) to pilot yourself around.
Elsewhere is an even more immersive map of Yosemite from 1883, above, which has been transformed into a three dimensional experience. A staggering two sims in size, the map shows the topography of the Sierra Nevadas in great detail, and hidden just underneath (you can dip down, as the prims are phantom) is the original map in two dimensions.
Two globes allow you an "inside" experience. One, pictured above, is a Celestial Globe from 1792, showing a map of the heavens, and there's also a World Globe from 1790. Both locations have seats allowing you to spin around. (Try them in mouselook.)
Near the landing point is the World Push Pin Map, where you can, well, stick in a pin in your home town and leave a comment (and read everyone else's). Other cool things include the Map Walk, a selection of over 150 maps (at a more normal size) from different places and time periods; the Tower of Maps, a huge cylindrical experience; a Japanese Scroll Map; a Grand Canyon Panorama (in layers to give a sense of depth—shown at the bottom of the post (and I'm there, a tiny dot on the left part of the walkway below the map!)); and the Museum, which is your not only your hub for teleporting around but also is a place where you can get tons of free maps for your Second Life decorating and enjoyment—40 in all—plus free orreys and spheres! If you want even more information—as this is in large measure an educational place—there are links to Rumsey's website, a rich resource.
P.S. Set your draw distance way up at David Rumsey Maps—512 meters if you can.