1. From the top of the building, tourists are able to clearly see Bangkok.
2. From the top of the building, tourists are able to see clearly Bangkok.
3. From the top of the building, tourists are able to see Bangkok clearly.
4. He slowly walked to the door.
5. He walked slowly to the door.
3 and 5 are correct :r: . The problem here is the position of clearly and slowly (which are adverbs of manner). To understand why 3 and 5 are correct, consider the following rules:
1. Adverbs of manner come after the main verb that they qualify.
2. The main verb must not be separated from the direct object.
Now consider each sentence again:
1. :w: Clearly does not come after the main verb see.
2. :w: Yes, this time clearly comes after the main verb, but it separates the main verb from the direct object (Bangkok), which is not permitted.
3. :r: This time clearly comes after the main verb without separating the main verb from the direct object - so no problem.
4. :w: Slowly does not come after the main verb walked.
5. :r: Now slowly is in the correct position, after the main verb. There is no direct object. The door is an indirect object preceded by the preposition to. An indirect object can be separated from the main verb.