Obo's Tower was located in the Mouse Quarter of Malaz City. It was considered to be just an empty ruin by many residents, though that was but an illusion. The mage Obo did indeed live in the tower's lower chambers.
The ruined tower had a jagged top that was high enough to appear to thrust through the clouds. The tower grounds were littered with leaves and tossed garbage, and a low stone wall encircled the tower grounds.
In The Bonehunters
On the night that Adjunct Tavore Paran's fleet carrying the Malaz 14th Army arrived in Malaz City, the twin gods Oponn appeared on the top of Obo's tower. With a clear vantage of the entire city, they looked forward to the night's games of push and pull. Later in the evening, Shadowthrone visited Obo in his tower, informing him of the intruders. The furious Obo slammed the door shut, and after a while, Shadowthrone heard the top of Obo's tower erupt with a fireball and the outraged screams of the Twins.
In Night of Knives
Once Kiska dived into the grounds, she appeared in a different world, where Obo's tower rose massive and undamaged without any surrounding buildings, just the countryside. This was due to the influence of the Shadow Moon that was taking place that night. However, once she jumped over the wall and out of the tower grounds, she reappeared in Malaz City as she knew it.