I wrote to Eidos complaining about the problem and this is what they answer:
Tomb Raider Underworld: Coastal Thailand Level
After the MAP ROOM where they spin a large structure using Thor’s Gauntlet for the first time, a lever is sometimes not appearing (Lara would normally jump onto the lever and use her bodyweight to make it move downwards).
To rectify this, players should either:
1R -Revert back to a previous save and playthrough again.
2. -If the user already has an SD card they can use the attached saves and instructions below (note – they will lose all treasures they have collected if they use these).
1. Unzip “20081124 TRU Wii NTSC save.rar”
2. Place the contents of the unzipped folder onto an SD card.
3. Ensure the Wii is off and insert the SD Card into the Wii.
4. Boot up the Wii without the disc in.
5. Go to the Wii Options -> Select Save Data -> Select Wii -> Select SD Card.
6. Select the TR:Underworld file and then select the option copy to Wii memory
7. After save is copied remove SD card and reboot the Wii.
8. Start the game and Load the Save.