This paper presents a novel multimodal virtual rehabilitation environment. Its design and implementation are based on principles related to intrinsic motivation and game design. The system consists of visual, acoustic, and haptic modalities. Elements contributing to intrinsic motivation are carefully joined in the three modalities to increase patients' motivation during the long process of rehabilitation. The message in a bottle (MIB) virtual scenario is designed to allow interplay between motor and cognitive challenges in the exercising patient. The user first needs to perform a motor action to receive a cognitive challenge that is finally solved by a second motor action. Visual feedback provides the most relevant information related to the task. Acoustic feedback consists of environmental sounds, music, and spoken instructions or encouraging statements for the patient. The haptic modality generates tactile information related to the environment and provides various modes of assistance for the patient's arm movements. The MIB scenario was evaluated with 16 stroke patients, who rated it positively using the Intrinsic Motivation Inventory questionnaire. Additionally, the MIB scenario seems to elicit higher motivation than a simpler pick-and-place training task.