For people used to playing NetHack on DOS/Windows and therefore used to the IBMGraphics feature, it can be a bit jarring to use the DECGraphics (low ASCII only) style, which doesn't distinguish between many dungeon features. Simply adding OPTIONS=IBMGraphics to ~/.nethackrc usually produces garbled output and there seems to be no reliable way to get IBMGraphics working. So here's another way to get IBM-like graphics.
First, you need to have a version of NetHack with Unicode support. And your shell needs UTF-8 support, which is fairly common nowadays. I recommend the version from nethack.alt.org, not only for the Unicode support but for the many other helpful features it has. Then, just add the following to your ~/.nethackrc file, replacing any OPTIONS=IBMGraphics or OPTIONS=DECGraphics lines:
DUNGEONSYMBOLS=0x0020 0x2502 0x2500 0x250C 0x2510 0x2514 0x2518 0x253C 0x2534 0x252C 0x2524 0x251C 0x00B7 0x25A0 0x25A0 0x002B 0x002B 0x2261 0x00B1 0x00B7 0x2591 0x2592 0x003C 0x003E 0x003C 0x003E 0x005F 0x007C 0x005C 0x0023 0x2320 0x2248 0x00B7 0x2248 0x00B7 0x00B7 0x0023 0x0023 0x0020 0x221E 0x2248