There are a number of dedicated PvP Zones around Tibia. PvP is allowed in these zones, even on no-pvp servers.
Deaths in PvP Zones will not result in any loss of items, exp or skills. The player will be teleported back to the temple.
All Guildhalls have a dedicated PvP Zone arena that can only be accessed by those who are invited into the Guildhall.
All towns have a PvP Zone arena.
Thais Knights Guild
Carlin Knights Guild
Kazordoon Fighting Pit
Abdendriel Bug Pen
Edron Magic Academy
Darashia Knights Guild
Port Hope Knights Guild
There are also a number of PvP Zones in the open world. These zones often require passing a protection zone to enter so they can not be exploited in real PvP.