Sometimes ideas for roleplaying are triggered by real life. Urban exploring (exploring abandoned industrial sites) and geocaching are two of these.
The characters should be created as modern people. A very realistic scenario will not have survivalists or expert marksmen but a well-prepared group will probably want one person with medical skills and wilderness or urban survival skills. If your characters are tougher, then they will have various outdoor skills (Riding, First Aid, Identify Plant, Herbalism) and the game is more about competent characters exploring places with /things/ in them.
Attributes are probably on the low-side, given our modern life style (nobody with Great strength or Superb Consitution); few people with gifts of Never Gets Lost. Faults will abound, however. Out of Shape, Relies only on GPS (Easily Lost), Paying Car Loan...
And unless you set your story in a magical or psi-world, you won't need supernormal powers.
If you do want a psychic kids or ghost-hunter scenario with a person as a medium or psychometry power (most likely low powered given the modern setting), then the easiest way to think about the power is as a "miniature character" with its own attributes, skills, gifts and faults.
See also The Unexplained to incorporate these powers.
Combat, Wounds & Healing
Combat takes a back seat in more modern games. Yes, if you see a crazed cannibale with a shotgun, your primary skill should be Running...
Depending on how cinematic your urban explorers are going to be, wounds and healing are more along the lines of falling damage or poisons.
Poisons should be rated for Potency from Terrible to Superb. Poison ivy would be Terrible to most people. Roll 4dF on the Potency and give some characters a chance to roll on a Health attribute to resist the effects. The character's rolled degree helps guide the GM to describe the effects (you stop and scratch for one level to closed airways at three levels difference). For people with bad reactions to some poisons, Potency should be raised. At lethal levels, the game then becomes a race to get some characters back to cell-phone range to call in the helicopter.
Falling damage can also be rated from Terrible (falling out a window at ground level) to Superb (down the hatch!) and may be mitigated by an Acrobatics roll or Strength roll. A low-level game will have third-story falls at Poor while for others this might be rated at Great.
Potency for Poisons and Falling damage have excellent write-ups for Fudge in "Grimtooth's Traps Too."
Character example, Dolores Ramirez, from Fudge: